[PATCH v2 0/2] clk: meson: MPLL fixes for Meson8b

[PATCH v2 0/2] clk: meson: MPLL fixes for Meson8b

[Jerome Brunet]

MPLL clocks have been recently added to the Meson8b clock driver: [0]

On meson8b boards this unfortunately causes a division by zero error which
is fixed by patch #1 in this series.

While investigating this I found that there also seems to be a 32bit
overflow in the calculation in rate_from_params(), which is fixed by
patch #2 in this series.

Changes since v1: [1]
 - Return an error code when the mpll parameters are out of the specified
   range.
 - As agreed with martin, use DIV_ROUND_UP_ULL instead of mul_u64_u32_div.

[0] http://lists.infradead.org/pipermail/linux-amlogic/2017-March/002757.html
[1] https://lkml.kernel.org/r/20170401130225.8811-1-martin.blumenstingl at googlemail.com

Martin Blumenstingl (2):
  clk: meson: mpll: fix division by zero in rate_from_params
  clk: meson: mpll: use 64bit math in rate_from_params

 drivers/clk/meson/clk-mpll.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

-- 
2.9.3

[PATCH v2 1/2] clk: meson: mpll: fix division by zero in rate_from_params

[Jerome Brunet]

From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

According to the public datasheet all register bits in HHI_MPLL_CNTL7,
HHI_MPLL_CNTL8 and HHI_MPLL_CNTL9 default to zero. On all GX SoCs these
seem to be initialized by the bootloader to some default value.
However, on my Meson8 board they are not initialized, leading to a
division by zero in rate_from_params as the math is:
(parent_rate * SDM_DEN) / ((SDM_DEN * 0) + 0)

According to the datasheet, the minimum n2 value is 4. The rate provided
by the clock when n2 is less than this minimum is unpredictable. In such
case, we report an error.

Although the rate_from_params function was only introduced recently the
original bug has been there for much longer. It was only exposed
recently when the MPLL clocks were added to the Meson8b clock driver.

Fixes: 1c50da4f27 ("clk: meson: add mpll support")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/meson/clk-mpll.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c
index 540dabe5adad..d9462b505dcc 100644
--- a/drivers/clk/meson/clk-mpll.c
+++ b/drivers/clk/meson/clk-mpll.c
@@ -65,18 +65,21 @@
 #include "clkc.h"
 
 #define SDM_DEN 16384
-#define SDM_MIN 1
-#define SDM_MAX 16383
 #define N2_MIN	4
 #define N2_MAX	511
 
 #define to_meson_clk_mpll(_hw) container_of(_hw, struct meson_clk_mpll, hw)
 
-static unsigned long rate_from_params(unsigned long parent_rate,
+static long rate_from_params(unsigned long parent_rate,
 				      unsigned long sdm,
 				      unsigned long n2)
 {
-	return (parent_rate * SDM_DEN) / ((SDM_DEN * n2) + sdm);
+	unsigned long divisor = (SDM_DEN * n2) + sdm;
+
+	if (n2 < N2_MIN)
+		return -EINVAL;
+
+	return (parent_rate * SDM_DEN) / divisor;
 }
 
 static void params_from_rate(unsigned long requested_rate,
@@ -89,17 +92,13 @@ static void params_from_rate(unsigned long requested_rate,
 
 	if (div < N2_MIN) {
 		*n2 = N2_MIN;
-		*sdm = SDM_MIN;
+		*sdm = 0;
 	} else if (div > N2_MAX) {
 		*n2 = N2_MAX;
-		*sdm = SDM_MAX;
+		*sdm = SDM_DEN - 1;
 	} else {
 		*n2 = div;
 		*sdm = DIV_ROUND_UP(rem * SDM_DEN, requested_rate);
-		if (*sdm < SDM_MIN)
-			*sdm = SDM_MIN;
-		else if (*sdm > SDM_MAX)
-			*sdm = SDM_MAX;
 	}
 }
 
@@ -109,6 +108,7 @@ static unsigned long mpll_recalc_rate(struct clk_hw *hw,
 	struct meson_clk_mpll *mpll = to_meson_clk_mpll(hw);
 	struct parm *p;
 	unsigned long reg, sdm, n2;
+	long rate;
 
 	p = &mpll->sdm;
 	reg = readl(mpll->base + p->reg_off);
@@ -118,7 +118,11 @@ static unsigned long mpll_recalc_rate(struct clk_hw *hw,
 	reg = readl(mpll->base + p->reg_off);
 	n2 = PARM_GET(p->width, p->shift, reg);
 
-	return rate_from_params(parent_rate, sdm, n2);
+	rate = rate_from_params(parent_rate, sdm, n2);
+	if (rate < 0)
+		return 0;
+
+	return rate;
 }
 
 static long mpll_round_rate(struct clk_hw *hw,
-- 
2.9.3

[PATCH v2 1/2] clk: meson: mpll: fix division by zero in rate_from_params

[Neil Armstrong]

On 04/07/2017 05:34 PM, Jerome Brunet wrote:
> From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> 
> According to the public datasheet all register bits in HHI_MPLL_CNTL7,
> HHI_MPLL_CNTL8 and HHI_MPLL_CNTL9 default to zero. On all GX SoCs these
> seem to be initialized by the bootloader to some default value.
> However, on my Meson8 board they are not initialized, leading to a
> division by zero in rate_from_params as the math is:
> (parent_rate * SDM_DEN) / ((SDM_DEN * 0) + 0)
> 
> According to the datasheet, the minimum n2 value is 4. The rate provided
> by the clock when n2 is less than this minimum is unpredictable. In such
> case, we report an error.
> 
> Although the rate_from_params function was only introduced recently the
> original bug has been there for much longer. It was only exposed
> recently when the MPLL clocks were added to the Meson8b clock driver.
> 
> Fixes: 1c50da4f27 ("clk: meson: add mpll support")
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
> ---
>  drivers/clk/meson/clk-mpll.c | 26 +++++++++++++++-----------
>  1 file changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c
> index 540dabe5adad..d9462b505dcc 100644
> --- a/drivers/clk/meson/clk-mpll.c
> +++ b/drivers/clk/meson/clk-mpll.c
> @@ -65,18 +65,21 @@
>  #include "clkc.h"
>  
>  #define SDM_DEN 16384
> -#define SDM_MIN 1
> -#define SDM_MAX 16383
>  #define N2_MIN	4
>  #define N2_MAX	511
>  
>  #define to_meson_clk_mpll(_hw) container_of(_hw, struct meson_clk_mpll, hw)
>  
> -static unsigned long rate_from_params(unsigned long parent_rate,
> +static long rate_from_params(unsigned long parent_rate,
>  				      unsigned long sdm,
>  				      unsigned long n2)
>  {
> -	return (parent_rate * SDM_DEN) / ((SDM_DEN * n2) + sdm);
> +	unsigned long divisor = (SDM_DEN * n2) + sdm;
> +
> +	if (n2 < N2_MIN)
> +		return -EINVAL;
> +
> +	return (parent_rate * SDM_DEN) / divisor;
>  }
>  
>  static void params_from_rate(unsigned long requested_rate,
> @@ -89,17 +92,13 @@ static void params_from_rate(unsigned long requested_rate,
>  
>  	if (div < N2_MIN) {
>  		*n2 = N2_MIN;
> -		*sdm = SDM_MIN;
> +		*sdm = 0;
>  	} else if (div > N2_MAX) {
>  		*n2 = N2_MAX;
> -		*sdm = SDM_MAX;
> +		*sdm = SDM_DEN - 1;
>  	} else {
>  		*n2 = div;
>  		*sdm = DIV_ROUND_UP(rem * SDM_DEN, requested_rate);
> -		if (*sdm < SDM_MIN)
> -			*sdm = SDM_MIN;
> -		else if (*sdm > SDM_MAX)
> -			*sdm = SDM_MAX;
>  	}
>  }
>  
> @@ -109,6 +108,7 @@ static unsigned long mpll_recalc_rate(struct clk_hw *hw,
>  	struct meson_clk_mpll *mpll = to_meson_clk_mpll(hw);
>  	struct parm *p;
>  	unsigned long reg, sdm, n2;
> +	long rate;
>  
>  	p = &mpll->sdm;
>  	reg = readl(mpll->base + p->reg_off);
> @@ -118,7 +118,11 @@ static unsigned long mpll_recalc_rate(struct clk_hw *hw,
>  	reg = readl(mpll->base + p->reg_off);
>  	n2 = PARM_GET(p->width, p->shift, reg);
>  
> -	return rate_from_params(parent_rate, sdm, n2);
> +	rate = rate_from_params(parent_rate, sdm, n2);
> +	if (rate < 0)
> +		return 0;
> +
> +	return rate;
>  }
>  
>  static long mpll_round_rate(struct clk_hw *hw,
> 

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>

[PATCH v2 2/2] clk: meson: mpll: use 64bit math in rate_from_params

[Jerome Brunet]

From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

On Meson8b the MPLL parent clock (fixed_pll) has a rate of 2550MHz.
Multiplying this with SDM_DEN results in a value greater than 32bits.
This is not a problem on the 64bit Meson GX SoCs, but it may result in
undefined behavior on the older 32bit Meson8b SoC.

While rate_from_params was only introduced recently to make the math
reusable from _round_rate and _recalc_rate the original bug exists much
longer.

Fixes: 1c50da4f27 ("clk: meson: add mpll support")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
[as discussed on the ml, use DIV_ROUND_UP_ULL]
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/meson/clk-mpll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c
index d9462b505dcc..39eab69fe51a 100644
--- a/drivers/clk/meson/clk-mpll.c
+++ b/drivers/clk/meson/clk-mpll.c
@@ -79,7 +79,7 @@ static long rate_from_params(unsigned long parent_rate,
 	if (n2 < N2_MIN)
 		return -EINVAL;
 
-	return (parent_rate * SDM_DEN) / divisor;
+	return DIV_ROUND_UP_ULL((u64)parent_rate * SDM_DEN, divisor);
 }
 
 static void params_from_rate(unsigned long requested_rate,
-- 
2.9.3

[PATCH v2 2/2] clk: meson: mpll: use 64bit math in rate_from_params

[Neil Armstrong]

On 04/07/2017 05:34 PM, Jerome Brunet wrote:
> From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> 
> On Meson8b the MPLL parent clock (fixed_pll) has a rate of 2550MHz.
> Multiplying this with SDM_DEN results in a value greater than 32bits.
> This is not a problem on the 64bit Meson GX SoCs, but it may result in
> undefined behavior on the older 32bit Meson8b SoC.
> 
> While rate_from_params was only introduced recently to make the math
> reusable from _round_rate and _recalc_rate the original bug exists much
> longer.
> 
> Fixes: 1c50da4f27 ("clk: meson: add mpll support")
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> [as discussed on the ml, use DIV_ROUND_UP_ULL]
> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
> ---
>  drivers/clk/meson/clk-mpll.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/meson/clk-mpll.c b/drivers/clk/meson/clk-mpll.c
> index d9462b505dcc..39eab69fe51a 100644
> --- a/drivers/clk/meson/clk-mpll.c
> +++ b/drivers/clk/meson/clk-mpll.c
> @@ -79,7 +79,7 @@ static long rate_from_params(unsigned long parent_rate,
>  	if (n2 < N2_MIN)
>  		return -EINVAL;
>  
> -	return (parent_rate * SDM_DEN) / divisor;
> +	return DIV_ROUND_UP_ULL((u64)parent_rate * SDM_DEN, divisor);
>  }
>  
>  static void params_from_rate(unsigned long requested_rate,
> 

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>