Re: [PATCHv4 2/2] mtd: spi-nor: cadence-quadspi: add reset control

[<Tudor.Ambarus@microchip.com>]

On 05/08/2019 04:43 PM, Dinh Nguyen wrote:
> Get the reset control properties for the QSPI controller and bring them
> out of reset. Most will have just one reset bit, but there is an additional
> OCP reset bit that is used ECC. The OCP reset bit will also need to get
> de-asserted as well. [1]
> 

It's always good to say why the change is needed, e.g. reset the controller at
init to have it in a clean state in case the bootloader messed with it.

> [1] https://www.intel.com/content/www/us/en/programmable/hps/arria-10/hps.html#reg_soc_top/sfo1429890575955.html
> 
> Suggested-by: Tien-Fong Chee <tien.fong.chee@intel.com>
> Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
> ---
> v4: fix compile error
> v3: return full error by using PTR_ERR(rtsc)
>     move reset control calls until after the clock enables
>     use udelay(2) to be safe
>     Add optional OCP(Open Core Protocol) reset signal
> v2: use devm_reset_control_get_optional_exclusive
>     print an error message
>     return -EPROBE_DEFER
> ---
>  drivers/mtd/spi-nor/cadence-quadspi.c | 30 +++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
> index 792628750eec..d3906e5a1d44 100644
> --- a/drivers/mtd/spi-nor/cadence-quadspi.c
> +++ b/drivers/mtd/spi-nor/cadence-quadspi.c
> @@ -34,6 +34,7 @@
>  #include <linux/of.h>
>  #include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/reset.h>
>  #include <linux/sched.h>
>  #include <linux/spi/spi.h>
>  #include <linux/timer.h>
> @@ -1336,6 +1337,8 @@ static int cqspi_probe(struct platform_device *pdev)
>  	struct cqspi_st *cqspi;
>  	struct resource *res;
>  	struct resource *res_ahb;
> +	struct reset_control *rstc;
> +	struct reset_control *rstc_ocp;
>  	const struct cqspi_driver_platdata *ddata;
>  	int ret;
>  	int irq;
> @@ -1402,6 +1405,33 @@ static int cqspi_probe(struct platform_device *pdev)
>  		goto probe_clk_failed;
>  	}
>  
> +	/* Obtain QSPI reset control */
> +	rstc = devm_reset_control_get_optional_exclusive(dev, "qspi");
> +	if (IS_ERR(rstc)) {
> +		dev_err(dev, "Cannot get QSPI reset.\n");
> +		if (PTR_ERR(rstc) == -EPROBE_DEFER)

what I meant was to get rid of this if and return PTR_ERR(rstc) directly.

> +			return PTR_ERR(rstc);
> +	}
> +
> +	rstc_ocp = devm_reset_control_get_optional_exclusive(dev, "qspi-ocp");
> +	if (IS_ERR(rstc_ocp)) {
> +		dev_err(dev, "Cannot get QSPI OCP reset.\n");
> +		if (PTR_ERR(rstc_ocp) == -EPROBE_DEFER)
> +			return PTR_ERR(rstc_ocp);
> +	}
> +
> +	if (rstc) {> +		reset_control_assert(rstc);
> +		udelay(2);

why 2us? what's the appropriate length of time that we should wait between
assert and deassert?

> +		reset_control_deassert(rstc);
> +	}
> +
> +	if (rstc_ocp) {
> +		reset_control_assert(rstc_ocp);

Does it mater the order in which you assert these signals? can we group these
module resets asserts, i.e. first do the assert for both rstc and rstcp and then
the deassert?

> +		udelay(2);
> +		reset_control_deassert(rstc_ocp);
Is software deassert needed? I'm looking at [2], Table 46. PER1 Group, Generated
Module Resets, and it seems that software deassert is not an option for
qspi_flash_ecc_rst_n

[2]https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/arria-10/a10_5v4.pdf

> +	}
> +
>  	cqspi->master_ref_clk_hz = clk_get_rate(cqspi->clk);
>  	ddata  = of_device_get_match_data(dev);
>  	if (ddata && (ddata->quirks & CQSPI_NEEDS_WR_DELAY))
>