drm/bridge: fix stack usage warning on old gcc

Message ID 20200428215408.4111675-1-arnd@arndb.de
State Accepted
Commit 78b0d99a68ecdc84728c99f4fef71942e9ecf35a
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Series
  • drm/bridge: fix stack usage warning on old gcc
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Commit Message

Arnd Bergmann April 28, 2020, 9:53 p.m.
Some older versions of gcc badly optimize code that passes
an inline function argument into another function by reference,
causing huge stack usage:

drivers/gpu/drm/bridge/tc358768.c: In function 'tc358768_bridge_pre_enable':
drivers/gpu/drm/bridge/tc358768.c:840:1: error: the frame size of 2256 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

Use a temporary variable as a workaround and add a comment pointing
to the gcc bug.

Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 drivers/gpu/drm/bridge/tc358768.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

-- 
2.26.0

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Comments

Tomi Valkeinen April 29, 2020, 7:56 a.m. | #1
On 29/04/2020 00:53, Arnd Bergmann wrote:
> Some older versions of gcc badly optimize code that passes

> an inline function argument into another function by reference,

> causing huge stack usage:

> 

> drivers/gpu/drm/bridge/tc358768.c: In function 'tc358768_bridge_pre_enable':

> drivers/gpu/drm/bridge/tc358768.c:840:1: error: the frame size of 2256 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

> 

> Use a temporary variable as a workaround and add a comment pointing

> to the gcc bug.

> 

> Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> ---

>   drivers/gpu/drm/bridge/tc358768.c | 4 +++-

>   1 file changed, 3 insertions(+), 1 deletion(-)

> 

> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c

> index 1b39e8d37834..6650fe4cfc20 100644

> --- a/drivers/gpu/drm/bridge/tc358768.c

> +++ b/drivers/gpu/drm/bridge/tc358768.c

> @@ -178,6 +178,8 @@ static int tc358768_clear_error(struct tc358768_priv *priv)

>   

>   static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)

>   {

> +	/* work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 */

> +	int tmpval = val;

>   	size_t count = 2;

>   

>   	if (priv->error)

> @@ -187,7 +189,7 @@ static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)

>   	if (reg < 0x100 || reg >= 0x600)

>   		count = 1;

>   

> -	priv->error = regmap_bulk_write(priv->regmap, reg, &val, count);

> +	priv->error = regmap_bulk_write(priv->regmap, reg, &tmpval, count);

>   }

>   

>   static void tc358768_read(struct tc358768_priv *priv, u32 reg, u32 *val)

> 


tc358768_write is not inline. What is the inline function here? Or is tc358768_write optimized to 
inline by the compiler?

  Tomi

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Arnd Bergmann April 29, 2020, 8:02 a.m. | #2
On Wed, Apr 29, 2020 at 9:56 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
> > diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c

> > index 1b39e8d37834..6650fe4cfc20 100644

> > --- a/drivers/gpu/drm/bridge/tc358768.c

> > +++ b/drivers/gpu/drm/bridge/tc358768.c

> > @@ -178,6 +178,8 @@ static int tc358768_clear_error(struct tc358768_priv *priv)

> >

> >   static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)

> >   {

> > +     /* work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 */

> > +     int tmpval = val;


>

> tc358768_write is not inline. What is the inline function here? Or is tc358768_write optimized to

> inline by the compiler?


I missed the lack of an explicit inline tag when looking at the bug. gcc
usually decides which functions to inline on its own, so there is little
difference in practice. Let me know if I should clarify the changelog and
resend it.

      Arnd
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Tomi Valkeinen April 29, 2020, 8:13 a.m. | #3
On 29/04/2020 11:02, Arnd Bergmann wrote:
> On Wed, Apr 29, 2020 at 9:56 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:

>>> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c

>>> index 1b39e8d37834..6650fe4cfc20 100644

>>> --- a/drivers/gpu/drm/bridge/tc358768.c

>>> +++ b/drivers/gpu/drm/bridge/tc358768.c

>>> @@ -178,6 +178,8 @@ static int tc358768_clear_error(struct tc358768_priv *priv)

>>>

>>>    static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)

>>>    {

>>> +     /* work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 */

>>> +     int tmpval = val;

> 

>>

>> tc358768_write is not inline. What is the inline function here? Or is tc358768_write optimized to

>> inline by the compiler?

> 

> I missed the lack of an explicit inline tag when looking at the bug. gcc

> usually decides which functions to inline on its own, so there is little

> difference in practice. Let me know if I should clarify the changelog and

> resend it.


Ok. I think this is fine.

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>


  Tomi

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Sam Ravnborg April 29, 2020, 8:46 p.m. | #4
Hi Arnd.

On Tue, Apr 28, 2020 at 11:53:54PM +0200, Arnd Bergmann wrote:
> Some older versions of gcc badly optimize code that passes

> an inline function argument into another function by reference,

> causing huge stack usage:

> 

> drivers/gpu/drm/bridge/tc358768.c: In function 'tc358768_bridge_pre_enable':

> drivers/gpu/drm/bridge/tc358768.c:840:1: error: the frame size of 2256 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

> 

> Use a temporary variable as a workaround and add a comment pointing

> to the gcc bug.

> 

> Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>


Thanks, pushed to drm-misc-next with Tomi's r-b.

	Sam

> ---

>  drivers/gpu/drm/bridge/tc358768.c | 4 +++-

>  1 file changed, 3 insertions(+), 1 deletion(-)

> 

> diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c

> index 1b39e8d37834..6650fe4cfc20 100644

> --- a/drivers/gpu/drm/bridge/tc358768.c

> +++ b/drivers/gpu/drm/bridge/tc358768.c

> @@ -178,6 +178,8 @@ static int tc358768_clear_error(struct tc358768_priv *priv)

>  

>  static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)

>  {

> +	/* work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 */

> +	int tmpval = val;

>  	size_t count = 2;

>  

>  	if (priv->error)

> @@ -187,7 +189,7 @@ static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)

>  	if (reg < 0x100 || reg >= 0x600)

>  		count = 1;

>  

> -	priv->error = regmap_bulk_write(priv->regmap, reg, &val, count);

> +	priv->error = regmap_bulk_write(priv->regmap, reg, &tmpval, count);

>  }

>  

>  static void tc358768_read(struct tc358768_priv *priv, u32 reg, u32 *val)

> -- 

> 2.26.0

> 

> _______________________________________________

> dri-devel mailing list

> dri-devel@lists.freedesktop.org

> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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Patch

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index 1b39e8d37834..6650fe4cfc20 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -178,6 +178,8 @@  static int tc358768_clear_error(struct tc358768_priv *priv)
 
 static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)
 {
+	/* work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 */
+	int tmpval = val;
 	size_t count = 2;
 
 	if (priv->error)
@@ -187,7 +189,7 @@  static void tc358768_write(struct tc358768_priv *priv, u32 reg, u32 val)
 	if (reg < 0x100 || reg >= 0x600)
 		count = 1;
 
-	priv->error = regmap_bulk_write(priv->regmap, reg, &val, count);
+	priv->error = regmap_bulk_write(priv->regmap, reg, &tmpval, count);
 }
 
 static void tc358768_read(struct tc358768_priv *priv, u32 reg, u32 *val)