Re: [PATCH v3 1/2] drm/fb-helper: Add multi buffer support for cma fbdev

[Daniel Vetter]

On Wed, Feb 22, 2017 at 04:49:01PM -0800, Maxime Ripard wrote:
> Hi Stefan,
> 
> On Mon, Feb 20, 2017 at 06:07:10PM +0100, Stefan Lengfeld wrote:
> > Hi Maxime,
> > 
> > sorry, I have missed the discussion about the double buffering/virtual
> > surface size patch series two weeks ago. My comments about the patch are
> > inline:
> > 
> > On Wed, Feb 15, 2017 at 05:19:08PM +0100, Maxime Ripard wrote:
> > > From: Xinliang Liu 
> > 
> > Mabye you should take the authorship here. Taking the credit and the
> > blame, because the patch was heavily modified by you and me. But I don't
> > really know what the offical police about that is.
> 
> I don't usually know when to do that as well. But yeah, you're
> probably right.

Sob line is the important bit, retaining original authorship is just
goodwill, and if in doubt showing more curtesy rarely hurts :-)

Patch applied to drm-misc, with Dave's ack after a quick irc discussion.
-Daniel

> 
> > > 
> > > This patch add a config to support to create multi buffer for cma fbdev.
> > > Such as double buffer and triple buffer.
> > > 
> > > Cma fbdev is convient to add a legency fbdev. And still many Android
> > > devices use fbdev now and at least double buffer is needed for these
> > > Android devices, so that a buffer flip can be operated. It will need
> > > some time for Android device vendors to abondon legency fbdev. So multi
> > > buffer for fbdev is needed.
> > > 
> > > Signed-off-by: Xinliang Liu 
> > > [s.chr...@phytec.de: Picking patch from
> > >  https://lkml.org/lkml/2015/9/14/188]
> > > Signed-off-by: Stefan Christ 
> > > Signed-off-by: Maxime Ripard 
> > 
> > Reviewed-by: Stefan Lengfeld 
> > 
> > My surname has changed from "Christ" to "Lengfeld" recently. So my
> > review tag contains the new name.
> 
> Ack
> 
> > 
> > > ---
> > >  drivers/gpu/drm/Kconfig |  9 +
> > >  drivers/gpu/drm/drm_fb_helper.c | 10 ++
> > >  2 files changed, 19 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > > index ebfe8404c25f..700c8b8e57a9 100644
> > > --- a/drivers/gpu/drm/Kconfig
> > > +++ b/drivers/gpu/drm/Kconfig
> > > @@ -84,6 +84,15 @@ config DRM_FBDEV_EMULATION
> > >  
> > > If in doubt, say "Y".
> > >  
> > > +config DRM_FBDEV_OVERALLOC
> > > + int "Overallocation of the fbdev buffer"
> > > + depends on DRM_FBDEV_EMULATION
> > > + default 100
> > > + help
> > > +   Defines the fbdev buffer overallocation in percent. Default
> > > +   is 100. Typical values for double buffering will be 200,
> > > +   triple buffering 300.
> > > +
> > >  config DRM_LOAD_EDID_FIRMWARE
> > >   bool "Allow to specify an EDID data set instead of probing for it"
> > >   depends on DRM_KMS_HELPER
> > > diff --git a/drivers/gpu/drm/drm_fb_helper.c 
> > > b/drivers/gpu/drm/drm_fb_helper.c
> > > index e934b541feea..c6de87abaca8 100644
> > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > @@ -48,6 +48,12 @@ module_param_named(fbdev_emulation, 
> > > drm_fbdev_emulation, bool, 0600);
> > >  MODULE_PARM_DESC(fbdev_emulation,
> > >"Enable legacy fbdev emulation [default=true]");
> > >  
> > > +static int drm_fbdev_overalloc = CONFIG_DRM_FBDEV_OVERALLOC;
> > > +module_param(drm_fbdev_overalloc, int, 0444);
> > 
> > Maybe the variable should be of type "uint" instead of "int". This would
> > rule out the negative numbers error case.
> 
> Yep, I'll change it.
> 
> > > +MODULE_PARM_DESC(drm_fbdev_overalloc,
> > > +  "Overallocation of the fbdev buffer (%) [default="
> > > +  __MODULE_STRING(CONFIG_DRM_FBDEV_OVERALLOC) "]");
> > > +
> > >  static LIST_HEAD(kernel_fb_helper_list);
> > >  static DEFINE_MUTEX(kernel_fb_helper_lock);
> > >  
> > > @@ -1573,6 +1579,10 @@ static int drm_fb_helper_single_fb_probe(struct 
> > > drm_fb_helper *fb_helper,
> > >   sizes.fb_height = sizes.surface_height = 768;
> > >   }
> > >  
> > > + /* Handle our overallocation */
> > > + sizes.surface_height *= drm_fbdev_overalloc;
> > > + sizes.surface_height /= 100;
> > > +
> > 
> > The code can trigger an arithmetic overflow, but I think we can ignore
> > this error case here.
> > 
> > But there should be a check for drm_fbdev_overalloc not be smaller than
> > 100. If it is smaller, the variable drm_fbdev_overalloc should have the
> > default value "100". Otherwise the virtual surface height can be smaller
> > than the physical height. This could trigger a lot of errors in existing
> > code paths.
> 
> That's a really good point, I'll change that.
> 
> Thanks!
> Maxime
> 
> -- 
> Maxime Ripard, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com



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Re: [PATCH v3 1/2] drm/fb-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

Hi Stefan,

On Mon, Feb 20, 2017 at 06:07:10PM +0100, Stefan Lengfeld wrote:
> Hi Maxime,
> 
> sorry, I have missed the discussion about the double buffering/virtual
> surface size patch series two weeks ago. My comments about the patch are
> inline:
> 
> On Wed, Feb 15, 2017 at 05:19:08PM +0100, Maxime Ripard wrote:
> > From: Xinliang Liu 
> 
> Mabye you should take the authorship here. Taking the credit and the
> blame, because the patch was heavily modified by you and me. But I don't
> really know what the offical police about that is.

I don't usually know when to do that as well. But yeah, you're
probably right.

> > 
> > This patch add a config to support to create multi buffer for cma fbdev.
> > Such as double buffer and triple buffer.
> > 
> > Cma fbdev is convient to add a legency fbdev. And still many Android
> > devices use fbdev now and at least double buffer is needed for these
> > Android devices, so that a buffer flip can be operated. It will need
> > some time for Android device vendors to abondon legency fbdev. So multi
> > buffer for fbdev is needed.
> > 
> > Signed-off-by: Xinliang Liu 
> > [s.chr...@phytec.de: Picking patch from
> >  https://lkml.org/lkml/2015/9/14/188]
> > Signed-off-by: Stefan Christ 
> > Signed-off-by: Maxime Ripard 
> 
> Reviewed-by: Stefan Lengfeld 
> 
> My surname has changed from "Christ" to "Lengfeld" recently. So my
> review tag contains the new name.

Ack

> 
> > ---
> >  drivers/gpu/drm/Kconfig |  9 +
> >  drivers/gpu/drm/drm_fb_helper.c | 10 ++
> >  2 files changed, 19 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index ebfe8404c25f..700c8b8e57a9 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -84,6 +84,15 @@ config DRM_FBDEV_EMULATION
> >  
> >   If in doubt, say "Y".
> >  
> > +config DRM_FBDEV_OVERALLOC
> > +   int "Overallocation of the fbdev buffer"
> > +   depends on DRM_FBDEV_EMULATION
> > +   default 100
> > +   help
> > + Defines the fbdev buffer overallocation in percent. Default
> > + is 100. Typical values for double buffering will be 200,
> > + triple buffering 300.
> > +
> >  config DRM_LOAD_EDID_FIRMWARE
> > bool "Allow to specify an EDID data set instead of probing for it"
> > depends on DRM_KMS_HELPER
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c 
> > b/drivers/gpu/drm/drm_fb_helper.c
> > index e934b541feea..c6de87abaca8 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -48,6 +48,12 @@ module_param_named(fbdev_emulation, drm_fbdev_emulation, 
> > bool, 0600);
> >  MODULE_PARM_DESC(fbdev_emulation,
> >  "Enable legacy fbdev emulation [default=true]");
> >  
> > +static int drm_fbdev_overalloc = CONFIG_DRM_FBDEV_OVERALLOC;
> > +module_param(drm_fbdev_overalloc, int, 0444);
> 
> Maybe the variable should be of type "uint" instead of "int". This would
> rule out the negative numbers error case.

Yep, I'll change it.

> > +MODULE_PARM_DESC(drm_fbdev_overalloc,
> > +"Overallocation of the fbdev buffer (%) [default="
> > +__MODULE_STRING(CONFIG_DRM_FBDEV_OVERALLOC) "]");
> > +
> >  static LIST_HEAD(kernel_fb_helper_list);
> >  static DEFINE_MUTEX(kernel_fb_helper_lock);
> >  
> > @@ -1573,6 +1579,10 @@ static int drm_fb_helper_single_fb_probe(struct 
> > drm_fb_helper *fb_helper,
> > sizes.fb_height = sizes.surface_height = 768;
> > }
> >  
> > +   /* Handle our overallocation */
> > +   sizes.surface_height *= drm_fbdev_overalloc;
> > +   sizes.surface_height /= 100;
> > +
> 
> The code can trigger an arithmetic overflow, but I think we can ignore
> this error case here.
> 
> But there should be a check for drm_fbdev_overalloc not be smaller than
> 100. If it is smaller, the variable drm_fbdev_overalloc should have the
> default value "100". Otherwise the virtual surface height can be smaller
> than the physical height. This could trigger a lot of errors in existing
> code paths.

That's a really good point, I'll change that.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com


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Re: [PATCH v3 1/2] drm/fb-helper: Add multi buffer support for cma fbdev

[Stefan Lengfeld]

Hi Maxime,

sorry, I have missed the discussion about the double buffering/virtual
surface size patch series two weeks ago. My comments about the patch are
inline:

On Wed, Feb 15, 2017 at 05:19:08PM +0100, Maxime Ripard wrote:
> From: Xinliang Liu 

Mabye you should take the authorship here. Taking the credit and the
blame, because the patch was heavily modified by you and me. But I don't
really know what the offical police about that is.

> 
> This patch add a config to support to create multi buffer for cma fbdev.
> Such as double buffer and triple buffer.
> 
> Cma fbdev is convient to add a legency fbdev. And still many Android
> devices use fbdev now and at least double buffer is needed for these
> Android devices, so that a buffer flip can be operated. It will need
> some time for Android device vendors to abondon legency fbdev. So multi
> buffer for fbdev is needed.
> 
> Signed-off-by: Xinliang Liu 
> [s.chr...@phytec.de: Picking patch from
>  https://lkml.org/lkml/2015/9/14/188]
> Signed-off-by: Stefan Christ 
> Signed-off-by: Maxime Ripard 

Reviewed-by: Stefan Lengfeld 

My surname has changed from "Christ" to "Lengfeld" recently. So my
review tag contains the new name.

> ---
>  drivers/gpu/drm/Kconfig |  9 +
>  drivers/gpu/drm/drm_fb_helper.c | 10 ++
>  2 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index ebfe8404c25f..700c8b8e57a9 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -84,6 +84,15 @@ config DRM_FBDEV_EMULATION
>  
> If in doubt, say "Y".
>  
> +config DRM_FBDEV_OVERALLOC
> + int "Overallocation of the fbdev buffer"
> + depends on DRM_FBDEV_EMULATION
> + default 100
> + help
> +   Defines the fbdev buffer overallocation in percent. Default
> +   is 100. Typical values for double buffering will be 200,
> +   triple buffering 300.
> +
>  config DRM_LOAD_EDID_FIRMWARE
>   bool "Allow to specify an EDID data set instead of probing for it"
>   depends on DRM_KMS_HELPER
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index e934b541feea..c6de87abaca8 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -48,6 +48,12 @@ module_param_named(fbdev_emulation, drm_fbdev_emulation, 
> bool, 0600);
>  MODULE_PARM_DESC(fbdev_emulation,
>"Enable legacy fbdev emulation [default=true]");
>  
> +static int drm_fbdev_overalloc = CONFIG_DRM_FBDEV_OVERALLOC;
> +module_param(drm_fbdev_overalloc, int, 0444);

Maybe the variable should be of type "uint" instead of "int". This would
rule out the negative numbers error case.

> +MODULE_PARM_DESC(drm_fbdev_overalloc,
> +  "Overallocation of the fbdev buffer (%) [default="
> +  __MODULE_STRING(CONFIG_DRM_FBDEV_OVERALLOC) "]");
> +
>  static LIST_HEAD(kernel_fb_helper_list);
>  static DEFINE_MUTEX(kernel_fb_helper_lock);
>  
> @@ -1573,6 +1579,10 @@ static int drm_fb_helper_single_fb_probe(struct 
> drm_fb_helper *fb_helper,
>   sizes.fb_height = sizes.surface_height = 768;
>   }
>  
> + /* Handle our overallocation */
> + sizes.surface_height *= drm_fbdev_overalloc;
> + sizes.surface_height /= 100;
> +

The code can trigger an arithmetic overflow, but I think we can ignore
this error case here.

But there should be a check for drm_fbdev_overalloc not be smaller than
100. If it is smaller, the variable drm_fbdev_overalloc should have the
default value "100". Otherwise the virtual surface height can be smaller
than the physical height. This could trigger a lot of errors in existing
code paths.

Kind regards,
Stefan Lengfeld

>   /* push down into drivers */
>   ret = (*fb_helper->funcs->fb_probe)(fb_helper, );
>   if (ret < 0)
> -- 
> git-series 0.8.11
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[PATCH v3 1/2] drm/fb-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

From: Xinliang Liu 

This patch add a config to support to create multi buffer for cma fbdev.
Such as double buffer and triple buffer.

Cma fbdev is convient to add a legency fbdev. And still many Android
devices use fbdev now and at least double buffer is needed for these
Android devices, so that a buffer flip can be operated. It will need
some time for Android device vendors to abondon legency fbdev. So multi
buffer for fbdev is needed.

Signed-off-by: Xinliang Liu 
[s.chr...@phytec.de: Picking patch from
 https://lkml.org/lkml/2015/9/14/188]
Signed-off-by: Stefan Christ 
Signed-off-by: Maxime Ripard 
---
 drivers/gpu/drm/Kconfig |  9 +
 drivers/gpu/drm/drm_fb_helper.c | 10 ++
 2 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index ebfe8404c25f..700c8b8e57a9 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -84,6 +84,15 @@ config DRM_FBDEV_EMULATION
 
  If in doubt, say "Y".
 
+config DRM_FBDEV_OVERALLOC
+   int "Overallocation of the fbdev buffer"
+   depends on DRM_FBDEV_EMULATION
+   default 100
+   help
+ Defines the fbdev buffer overallocation in percent. Default
+ is 100. Typical values for double buffering will be 200,
+ triple buffering 300.
+
 config DRM_LOAD_EDID_FIRMWARE
bool "Allow to specify an EDID data set instead of probing for it"
depends on DRM_KMS_HELPER
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index e934b541feea..c6de87abaca8 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -48,6 +48,12 @@ module_param_named(fbdev_emulation, drm_fbdev_emulation, 
bool, 0600);
 MODULE_PARM_DESC(fbdev_emulation,
 "Enable legacy fbdev emulation [default=true]");
 
+static int drm_fbdev_overalloc = CONFIG_DRM_FBDEV_OVERALLOC;
+module_param(drm_fbdev_overalloc, int, 0444);
+MODULE_PARM_DESC(drm_fbdev_overalloc,
+"Overallocation of the fbdev buffer (%) [default="
+__MODULE_STRING(CONFIG_DRM_FBDEV_OVERALLOC) "]");
+
 static LIST_HEAD(kernel_fb_helper_list);
 static DEFINE_MUTEX(kernel_fb_helper_lock);
 
@@ -1573,6 +1579,10 @@ static int drm_fb_helper_single_fb_probe(struct 
drm_fb_helper *fb_helper,
sizes.fb_height = sizes.surface_height = 768;
}
 
+   /* Handle our overallocation */
+   sizes.surface_height *= drm_fbdev_overalloc;
+   sizes.surface_height /= 100;
+
/* push down into drivers */
ret = (*fb_helper->funcs->fb_probe)(fb_helper, );
if (ret < 0)
-- 
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