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 <xinliang.liu@xxxxxxxxxx> > > 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 <xinliang.liu@xxxxxxxxxx> > > [s.christ@xxxxxxxxx: Picking patch from > > https://lkml.org/lkml/2015/9/14/188] > > Signed-off-by: Stefan Christ <s.christ@xxxxxxxxx> > > Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> > > Reviewed-by: Stefan Lengfeld <contact@xxxxxxxxxxxxxxx> > > 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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