[PATCH STABLE v4.4+] pwm: fsl-ftm: Use flat regmap cache

[PATCH STABLE v4.4+] pwm: fsl-ftm: Use flat regmap cache

[Krzysztof Kozlowski]

From: Stefan Agner <stefan@agner.ch>

commit ad06fdeeef1cbadf86ebbe510e8079abada8b44e upstream.

Use flat regmap cache to avoid lockdep warning at probe:

[    0.697285] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x15c/0x160()
[    0.697449] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))

The RB-tree regmap cache needs to allocate new space on first writes.
However, allocations in an atomic context (e.g. when a spinlock is held)
are not allowed. The function regmap_write calls map->lock, which
acquires a spinlock in the fast_io case. Since the pwm-fsl-ftm driver
uses MMIO, the regmap bus of type regmap_mmio is being used which has
fast_io set to true.

The MMIO space of the pwm-fsl-ftm driver is reasonable condense, hence
using the much faster flat regmap cache is anyway the better choice.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

---

Fixes lockdep warning. Apply to v4.4 and newer.
---
 drivers/pwm/pwm-fsl-ftm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-fsl-ftm.c b/drivers/pwm/pwm-fsl-ftm.c
index 7225ac6b3df5..fad968eb75f6 100644
--- a/drivers/pwm/pwm-fsl-ftm.c
+++ b/drivers/pwm/pwm-fsl-ftm.c
@@ -392,7 +392,7 @@ static const struct regmap_config fsl_pwm_regmap_config = {
 
 	.max_register = FTM_PWMLOAD,
 	.volatile_reg = fsl_pwm_volatile_reg,
-	.cache_type = REGCACHE_RBTREE,
+	.cache_type = REGCACHE_FLAT,
 };
 
 static int fsl_pwm_probe(struct platform_device *pdev)
-- 
2.17.1

Re: [PATCH STABLE v4.4+] pwm: fsl-ftm: Use flat regmap cache

[Greg KH]

On Tue, Jun 09, 2020 at 04:35:17PM +0200, Krzysztof Kozlowski wrote:
> From: Stefan Agner <stefan@agner.ch>
> 
> commit ad06fdeeef1cbadf86ebbe510e8079abada8b44e upstream.
> 
> Use flat regmap cache to avoid lockdep warning at probe:
> 
> [    0.697285] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x15c/0x160()
> [    0.697449] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> 
> The RB-tree regmap cache needs to allocate new space on first writes.
> However, allocations in an atomic context (e.g. when a spinlock is held)
> are not allowed. The function regmap_write calls map->lock, which
> acquires a spinlock in the fast_io case. Since the pwm-fsl-ftm driver
> uses MMIO, the regmap bus of type regmap_mmio is being used which has
> fast_io set to true.
> 
> The MMIO space of the pwm-fsl-ftm driver is reasonable condense, hence
> using the much faster flat regmap cache is anyway the better choice.
> 
> Signed-off-by: Stefan Agner <stefan@agner.ch>
> Cc: Mark Brown <broonie@kernel.org>
> Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
> Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
> 
> ---
> 
> Fixes lockdep warning. Apply to v4.4 and newer.
> ---
>  drivers/pwm/pwm-fsl-ftm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-fsl-ftm.c b/drivers/pwm/pwm-fsl-ftm.c
> index 7225ac6b3df5..fad968eb75f6 100644
> --- a/drivers/pwm/pwm-fsl-ftm.c
> +++ b/drivers/pwm/pwm-fsl-ftm.c
> @@ -392,7 +392,7 @@ static const struct regmap_config fsl_pwm_regmap_config = {
>  
>  	.max_register = FTM_PWMLOAD,
>  	.volatile_reg = fsl_pwm_volatile_reg,
> -	.cache_type = REGCACHE_RBTREE,
> +	.cache_type = REGCACHE_FLAT,
>  };
>  
>  static int fsl_pwm_probe(struct platform_device *pdev)
> -- 
> 2.17.1
> 

Now queued up, thanks.

greg k-h