* [PATCHv3 03/16] irqchip: irq-armada-370-xp: suspend/resume support
[not found] <1416585613-2113-1-git-send-email-thomas.petazzoni@free-electrons.com>
@ 2014-11-21 16:00 ` Thomas Petazzoni
2014-11-21 16:00 ` [PATCHv3 04/16] clocksource: time-armada-370-xp: add " Thomas Petazzoni
2014-11-21 16:00 ` [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks Thomas Petazzoni
2 siblings, 0 replies; 6+ messages in thread
From: Thomas Petazzoni @ 2014-11-21 16:00 UTC (permalink / raw)
To: Jason Cooper, Andrew Lunn, Sebastian Hesselbarth, Gregory Clement
Cc: linux-arm-kernel, Tawfik Bayouk, Nadav Haklai, Lior Amsalem,
Ezequiel Garcia, devicetree, Thomas Petazzoni, Thomas Gleixner,
linux-kernel
This commit adds suspend/resume support to the irqchip driver used on
Armada XP platforms (amongst others). It does so by adding a set of
suspend/resume syscore_ops, that will respectively save and restore
the necessary registers to ensure interrupts continue to work after
resume.
It is worth mentioning that the affinity is lost during a
suspend/resume cycle, because when a secondary CPU is brought
off-line, all interrupts that are assigned to this CPU in terms of
affinity gets re-assigned to a still running CPU. Therefore, right
before entering suspend, all interrupts are assigned to the boot CPU.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: linux-kernel@vger.kernel.org
---
drivers/irqchip/irq-armada-370-xp.c | 52 +++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/drivers/irqchip/irq-armada-370-xp.c b/drivers/irqchip/irq-armada-370-xp.c
index 3e238cd..4ec137b 100644
--- a/drivers/irqchip/irq-armada-370-xp.c
+++ b/drivers/irqchip/irq-armada-370-xp.c
@@ -26,6 +26,7 @@
#include <linux/of_pci.h>
#include <linux/irqdomain.h>
#include <linux/slab.h>
+#include <linux/syscore_ops.h>
#include <linux/msi.h>
#include <asm/mach/arch.h>
#include <asm/exception.h>
@@ -66,6 +67,7 @@
static void __iomem *per_cpu_int_base;
static void __iomem *main_int_base;
static struct irq_domain *armada_370_xp_mpic_domain;
+static u32 doorbell_mask_reg;
#ifdef CONFIG_PCI_MSI
static struct irq_domain *armada_370_xp_msi_domain;
static DECLARE_BITMAP(msi_used, PCI_MSI_DOORBELL_NR);
@@ -474,6 +476,54 @@ armada_370_xp_handle_irq(struct pt_regs *regs)
} while (1);
}
+static int armada_370_xp_mpic_suspend(void)
+{
+ doorbell_mask_reg = readl(per_cpu_int_base +
+ ARMADA_370_XP_IN_DRBEL_MSK_OFFS);
+ return 0;
+}
+
+static void armada_370_xp_mpic_resume(void)
+{
+ int nirqs;
+ irq_hw_number_t irq;
+
+ /* Re-enable interrupts */
+ nirqs = (readl(main_int_base + ARMADA_370_XP_INT_CONTROL) >> 2) & 0x3ff;
+ for (irq = 0; irq < nirqs; irq++) {
+ struct irq_data *data;
+ int virq;
+
+ virq = irq_linear_revmap(armada_370_xp_mpic_domain, irq);
+ if (virq == 0)
+ continue;
+
+ if (irq != ARMADA_370_XP_TIMER0_PER_CPU_IRQ)
+ writel(irq, per_cpu_int_base +
+ ARMADA_370_XP_INT_CLEAR_MASK_OFFS);
+ else
+ writel(irq, main_int_base +
+ ARMADA_370_XP_INT_SET_ENABLE_OFFS);
+
+ data = irq_get_irq_data(virq);
+ if (!irqd_irq_disabled(data))
+ armada_370_xp_irq_unmask(data);
+ }
+
+ /* Reconfigure doorbells for IPIs and MSIs */
+ writel(doorbell_mask_reg,
+ per_cpu_int_base + ARMADA_370_XP_IN_DRBEL_MSK_OFFS);
+ if (doorbell_mask_reg & IPI_DOORBELL_MASK)
+ writel(0, per_cpu_int_base + ARMADA_370_XP_INT_CLEAR_MASK_OFFS);
+ if (doorbell_mask_reg & PCI_MSI_DOORBELL_MASK)
+ writel(1, per_cpu_int_base + ARMADA_370_XP_INT_CLEAR_MASK_OFFS);
+}
+
+struct syscore_ops armada_370_xp_mpic_syscore_ops = {
+ .suspend = armada_370_xp_mpic_suspend,
+ .resume = armada_370_xp_mpic_resume,
+};
+
static int __init armada_370_xp_mpic_of_init(struct device_node *node,
struct device_node *parent)
{
@@ -530,6 +580,8 @@ static int __init armada_370_xp_mpic_of_init(struct device_node *node,
armada_370_xp_mpic_handle_cascade_irq);
}
+ register_syscore_ops(&armada_370_xp_mpic_syscore_ops);
+
return 0;
}
--
2.1.0
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCHv3 04/16] clocksource: time-armada-370-xp: add suspend/resume support
[not found] <1416585613-2113-1-git-send-email-thomas.petazzoni@free-electrons.com>
2014-11-21 16:00 ` [PATCHv3 03/16] irqchip: irq-armada-370-xp: suspend/resume support Thomas Petazzoni
@ 2014-11-21 16:00 ` Thomas Petazzoni
2014-11-21 16:00 ` [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks Thomas Petazzoni
2 siblings, 0 replies; 6+ messages in thread
From: Thomas Petazzoni @ 2014-11-21 16:00 UTC (permalink / raw)
To: Jason Cooper, Andrew Lunn, Sebastian Hesselbarth, Gregory Clement
Cc: linux-arm-kernel, Tawfik Bayouk, Nadav Haklai, Lior Amsalem,
Ezequiel Garcia, devicetree, Thomas Petazzoni, Daniel Lezcano,
Thomas Gleixner, linux-kernel
This commit adds a set of suspend/resume syscore_ops to respectively
save and restore a number of timer registers, in order to make sure
the clockevent and clocksource devices continue to work properly
across a suspend/resume cycle.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
drivers/clocksource/time-armada-370-xp.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/drivers/clocksource/time-armada-370-xp.c b/drivers/clocksource/time-armada-370-xp.c
index 0451e62..ff37d3a 100644
--- a/drivers/clocksource/time-armada-370-xp.c
+++ b/drivers/clocksource/time-armada-370-xp.c
@@ -43,6 +43,7 @@
#include <linux/module.h>
#include <linux/sched_clock.h>
#include <linux/percpu.h>
+#include <linux/syscore_ops.h>
/*
* Timer block registers.
@@ -223,6 +224,28 @@ static struct notifier_block armada_370_xp_timer_cpu_nb = {
.notifier_call = armada_370_xp_timer_cpu_notify,
};
+static u32 timer0_ctrl_reg, timer0_local_ctrl_reg;
+
+static int armada_370_xp_timer_suspend(void)
+{
+ timer0_ctrl_reg = readl(timer_base + TIMER_CTRL_OFF);
+ timer0_local_ctrl_reg = readl(local_base + TIMER_CTRL_OFF);
+ return 0;
+}
+
+static void armada_370_xp_timer_resume(void)
+{
+ writel(0xffffffff, timer_base + TIMER0_VAL_OFF);
+ writel(0xffffffff, timer_base + TIMER0_RELOAD_OFF);
+ writel(timer0_ctrl_reg, timer_base + TIMER_CTRL_OFF);
+ writel(timer0_local_ctrl_reg, local_base + TIMER_CTRL_OFF);
+}
+
+struct syscore_ops armada_370_xp_timer_syscore_ops = {
+ .suspend = armada_370_xp_timer_suspend,
+ .resume = armada_370_xp_timer_resume,
+};
+
static void __init armada_370_xp_timer_common_init(struct device_node *np)
{
u32 clr = 0, set = 0;
@@ -285,6 +308,8 @@ static void __init armada_370_xp_timer_common_init(struct device_node *np)
/* Immediately configure the timer on the boot CPU */
if (!res)
armada_370_xp_timer_setup(this_cpu_ptr(armada_370_xp_evt));
+
+ register_syscore_ops(&armada_370_xp_timer_syscore_ops);
}
static void __init armada_xp_timer_init(struct device_node *np)
--
2.1.0
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks
[not found] <1416585613-2113-1-git-send-email-thomas.petazzoni@free-electrons.com>
2014-11-21 16:00 ` [PATCHv3 03/16] irqchip: irq-armada-370-xp: suspend/resume support Thomas Petazzoni
2014-11-21 16:00 ` [PATCHv3 04/16] clocksource: time-armada-370-xp: add " Thomas Petazzoni
@ 2014-11-21 16:00 ` Thomas Petazzoni
2014-11-25 6:07 ` Mike Turquette
2 siblings, 1 reply; 6+ messages in thread
From: Thomas Petazzoni @ 2014-11-21 16:00 UTC (permalink / raw)
To: Jason Cooper, Andrew Lunn, Sebastian Hesselbarth, Gregory Clement
Cc: linux-arm-kernel, Tawfik Bayouk, Nadav Haklai, Lior Amsalem,
Ezequiel Garcia, devicetree, Thomas Petazzoni, Mike Turquette,
linux-kernel
This commit adds suspend/resume support for the gatable clock driver
used on Marvell EBU platforms. When getting out of suspend, the
Marvell EBU platforms go through the bootloader, which re-enables all
gatable clocks. However, upon resume, the clock framework will not
disable again all gatable clocks that are not used.
Therefore, if the clock driver does not save/restore the state of the
gatable clocks, all gatable clocks that are not claimed by any device
driver will remain enabled after a resume. This is why this driver
saves and restores the state of those clocks.
Since clocks aren't real devices, we don't have the normal ->suspend()
and ->resume() of the device model, and have to use the ->suspend()
and ->resume() hooks of the syscore_ops mechanism. This mechanism has
the unfortunate idea of not providing a way of passing private data,
which requires us to change the driver to make the assumption that
there is only once instance of the gatable clock control structure.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Mike Turquette <mturquette@linaro.org>
Cc: linux-kernel@vger.kernel.org
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
---
drivers/clk/mvebu/common.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)
diff --git a/drivers/clk/mvebu/common.c b/drivers/clk/mvebu/common.c
index b7fcb46..0d4d121 100644
--- a/drivers/clk/mvebu/common.c
+++ b/drivers/clk/mvebu/common.c
@@ -19,6 +19,7 @@
#include <linux/io.h>
#include <linux/of.h>
#include <linux/of_address.h>
+#include <linux/syscore_ops.h>
#include "common.h"
@@ -177,14 +178,17 @@ struct clk_gating_ctrl {
spinlock_t *lock;
struct clk **gates;
int num_gates;
+ void __iomem *base;
+ u32 saved_reg;
};
#define to_clk_gate(_hw) container_of(_hw, struct clk_gate, hw)
+static struct clk_gating_ctrl *ctrl;
+
static struct clk *clk_gating_get_src(
struct of_phandle_args *clkspec, void *data)
{
- struct clk_gating_ctrl *ctrl = (struct clk_gating_ctrl *)data;
int n;
if (clkspec->args_count < 1)
@@ -199,15 +203,35 @@ static struct clk *clk_gating_get_src(
return ERR_PTR(-ENODEV);
}
+static int mvebu_clk_gating_suspend(void)
+{
+ ctrl->saved_reg = readl(ctrl->base);
+ return 0;
+}
+
+static void mvebu_clk_gating_resume(void)
+{
+ writel(ctrl->saved_reg, ctrl->base);
+}
+
+static struct syscore_ops clk_gate_syscore_ops = {
+ .suspend = mvebu_clk_gating_suspend,
+ .resume = mvebu_clk_gating_resume,
+};
+
void __init mvebu_clk_gating_setup(struct device_node *np,
const struct clk_gating_soc_desc *desc)
{
- struct clk_gating_ctrl *ctrl;
struct clk *clk;
void __iomem *base;
const char *default_parent = NULL;
int n;
+ if (ctrl) {
+ pr_err("mvebu-clk-gating: cannot instantiate more than one gatable clock device\n");
+ return;
+ }
+
base = of_iomap(np, 0);
if (WARN_ON(!base))
return;
@@ -225,6 +249,8 @@ void __init mvebu_clk_gating_setup(struct device_node *np,
/* lock must already be initialized */
ctrl->lock = &ctrl_gating_lock;
+ ctrl->base = base;
+
/* Count, allocate, and register clock gates */
for (n = 0; desc[n].name;)
n++;
@@ -246,6 +272,8 @@ void __init mvebu_clk_gating_setup(struct device_node *np,
of_clk_add_provider(np, clk_gating_get_src, ctrl);
+ register_syscore_ops(&clk_gate_syscore_ops);
+
return;
gates_out:
kfree(ctrl);
--
2.1.0
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks
2014-11-21 16:00 ` [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks Thomas Petazzoni
@ 2014-11-25 6:07 ` Mike Turquette
2014-11-25 6:48 ` Thomas Petazzoni
0 siblings, 1 reply; 6+ messages in thread
From: Mike Turquette @ 2014-11-25 6:07 UTC (permalink / raw)
To: Thomas Petazzoni, Jason Cooper, Andrew Lunn,
Sebastian Hesselbarth, Gregory Clement
Cc: linux-arm-kernel, Tawfik Bayouk, Nadav Haklai, Lior Amsalem,
Ezequiel Garcia, devicetree, Thomas Petazzoni, linux-kernel
Quoting Thomas Petazzoni (2014-11-21 08:00:05)
> This commit adds suspend/resume support for the gatable clock driver
> used on Marvell EBU platforms. When getting out of suspend, the
> Marvell EBU platforms go through the bootloader, which re-enables all
> gatable clocks. However, upon resume, the clock framework will not
> disable again all gatable clocks that are not used.
>
> Therefore, if the clock driver does not save/restore the state of the
> gatable clocks, all gatable clocks that are not claimed by any device
> driver will remain enabled after a resume. This is why this driver
> saves and restores the state of those clocks.
>
> Since clocks aren't real devices, we don't have the normal ->suspend()
> and ->resume() of the device model, and have to use the ->suspend()
> and ->resume() hooks of the syscore_ops mechanism. This mechanism has
> the unfortunate idea of not providing a way of passing private data,
> which requires us to change the driver to make the assumption that
> there is only once instance of the gatable clock control structure.
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Cc: Mike Turquette <mturquette@linaro.org>
> Cc: linux-kernel@vger.kernel.org
> Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Looks good to me. Which tree do you plan to take this through?
Regards,
Mike
> ---
> drivers/clk/mvebu/common.c | 32 ++++++++++++++++++++++++++++++--
> 1 file changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/mvebu/common.c b/drivers/clk/mvebu/common.c
> index b7fcb46..0d4d121 100644
> --- a/drivers/clk/mvebu/common.c
> +++ b/drivers/clk/mvebu/common.c
> @@ -19,6 +19,7 @@
> #include <linux/io.h>
> #include <linux/of.h>
> #include <linux/of_address.h>
> +#include <linux/syscore_ops.h>
>
> #include "common.h"
>
> @@ -177,14 +178,17 @@ struct clk_gating_ctrl {
> spinlock_t *lock;
> struct clk **gates;
> int num_gates;
> + void __iomem *base;
> + u32 saved_reg;
> };
>
> #define to_clk_gate(_hw) container_of(_hw, struct clk_gate, hw)
>
> +static struct clk_gating_ctrl *ctrl;
> +
> static struct clk *clk_gating_get_src(
> struct of_phandle_args *clkspec, void *data)
> {
> - struct clk_gating_ctrl *ctrl = (struct clk_gating_ctrl *)data;
> int n;
>
> if (clkspec->args_count < 1)
> @@ -199,15 +203,35 @@ static struct clk *clk_gating_get_src(
> return ERR_PTR(-ENODEV);
> }
>
> +static int mvebu_clk_gating_suspend(void)
> +{
> + ctrl->saved_reg = readl(ctrl->base);
> + return 0;
> +}
> +
> +static void mvebu_clk_gating_resume(void)
> +{
> + writel(ctrl->saved_reg, ctrl->base);
> +}
> +
> +static struct syscore_ops clk_gate_syscore_ops = {
> + .suspend = mvebu_clk_gating_suspend,
> + .resume = mvebu_clk_gating_resume,
> +};
> +
> void __init mvebu_clk_gating_setup(struct device_node *np,
> const struct clk_gating_soc_desc *desc)
> {
> - struct clk_gating_ctrl *ctrl;
> struct clk *clk;
> void __iomem *base;
> const char *default_parent = NULL;
> int n;
>
> + if (ctrl) {
> + pr_err("mvebu-clk-gating: cannot instantiate more than one gatable clock device\n");
> + return;
> + }
> +
> base = of_iomap(np, 0);
> if (WARN_ON(!base))
> return;
> @@ -225,6 +249,8 @@ void __init mvebu_clk_gating_setup(struct device_node *np,
> /* lock must already be initialized */
> ctrl->lock = &ctrl_gating_lock;
>
> + ctrl->base = base;
> +
> /* Count, allocate, and register clock gates */
> for (n = 0; desc[n].name;)
> n++;
> @@ -246,6 +272,8 @@ void __init mvebu_clk_gating_setup(struct device_node *np,
>
> of_clk_add_provider(np, clk_gating_get_src, ctrl);
>
> + register_syscore_ops(&clk_gate_syscore_ops);
> +
> return;
> gates_out:
> kfree(ctrl);
> --
> 2.1.0
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks
2014-11-25 6:07 ` Mike Turquette
@ 2014-11-25 6:48 ` Thomas Petazzoni
2014-11-26 4:03 ` Jason Cooper
0 siblings, 1 reply; 6+ messages in thread
From: Thomas Petazzoni @ 2014-11-25 6:48 UTC (permalink / raw)
To: Mike Turquette
Cc: Jason Cooper, Andrew Lunn, Sebastian Hesselbarth,
Gregory Clement, linux-arm-kernel, Tawfik Bayouk, Nadav Haklai,
Lior Amsalem, Ezequiel Garcia, devicetree, linux-kernel
Mike,
On Mon, 24 Nov 2014 22:07:00 -0800, Mike Turquette wrote:
> Quoting Thomas Petazzoni (2014-11-21 08:00:05)
> > This commit adds suspend/resume support for the gatable clock driver
> > used on Marvell EBU platforms. When getting out of suspend, the
> > Marvell EBU platforms go through the bootloader, which re-enables all
> > gatable clocks. However, upon resume, the clock framework will not
> > disable again all gatable clocks that are not used.
> >
> > Therefore, if the clock driver does not save/restore the state of the
> > gatable clocks, all gatable clocks that are not claimed by any device
> > driver will remain enabled after a resume. This is why this driver
> > saves and restores the state of those clocks.
> >
> > Since clocks aren't real devices, we don't have the normal ->suspend()
> > and ->resume() of the device model, and have to use the ->suspend()
> > and ->resume() hooks of the syscore_ops mechanism. This mechanism has
> > the unfortunate idea of not providing a way of passing private data,
> > which requires us to change the driver to make the assumption that
> > there is only once instance of the gatable clock control structure.
> >
> > Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> > Cc: Mike Turquette <mturquette@linaro.org>
> > Cc: linux-kernel@vger.kernel.org
> > Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
>
> Looks good to me. Which tree do you plan to take this through?
I don't have any specific plans. Jason, do you have other clk changes
for 3.19, which justify a pull request from you to Mike? Or could Mike
just take this patch in his tree? There is no build dependency between
this patch and the other patches in the series, so it can go through
whatever tree.
Thanks,
Thomas
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCHv3 08/16] clk: mvebu: add suspend/resume for gatable clocks
2014-11-25 6:48 ` Thomas Petazzoni
@ 2014-11-26 4:03 ` Jason Cooper
0 siblings, 0 replies; 6+ messages in thread
From: Jason Cooper @ 2014-11-26 4:03 UTC (permalink / raw)
To: Thomas Petazzoni
Cc: Mike Turquette, Andrew Lunn, Sebastian Hesselbarth,
Gregory Clement, linux-arm-kernel, Tawfik Bayouk, Nadav Haklai,
Lior Amsalem, Ezequiel Garcia, devicetree, linux-kernel
On Tue, Nov 25, 2014 at 07:48:01AM +0100, Thomas Petazzoni wrote:
> Mike,
>
> On Mon, 24 Nov 2014 22:07:00 -0800, Mike Turquette wrote:
> > Quoting Thomas Petazzoni (2014-11-21 08:00:05)
> > > This commit adds suspend/resume support for the gatable clock driver
> > > used on Marvell EBU platforms. When getting out of suspend, the
> > > Marvell EBU platforms go through the bootloader, which re-enables all
> > > gatable clocks. However, upon resume, the clock framework will not
> > > disable again all gatable clocks that are not used.
> > >
> > > Therefore, if the clock driver does not save/restore the state of the
> > > gatable clocks, all gatable clocks that are not claimed by any device
> > > driver will remain enabled after a resume. This is why this driver
> > > saves and restores the state of those clocks.
> > >
> > > Since clocks aren't real devices, we don't have the normal ->suspend()
> > > and ->resume() of the device model, and have to use the ->suspend()
> > > and ->resume() hooks of the syscore_ops mechanism. This mechanism has
> > > the unfortunate idea of not providing a way of passing private data,
> > > which requires us to change the driver to make the assumption that
> > > there is only once instance of the gatable clock control structure.
> > >
> > > Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> > > Cc: Mike Turquette <mturquette@linaro.org>
> > > Cc: linux-kernel@vger.kernel.org
> > > Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
> >
> > Looks good to me. Which tree do you plan to take this through?
>
> I don't have any specific plans. Jason, do you have other clk changes
> for 3.19, which justify a pull request from you to Mike? Or could Mike
> just take this patch in his tree? There is no build dependency between
> this patch and the other patches in the series, so it can go through
> whatever tree.
Well, I pulled the whole series into mvebu/soc-suspend to give it some
time in -next. It'd be easiest, with my current schedule, to send a
PR for it as-is. If that's ok with Mike, I'd appreciate it. Obviously,
I wouldn't make a habit of it... :-P
thx,
Jason.
^ permalink raw reply [flat|nested] 6+ messages in thread