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. > > 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. > --- > 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, &sizes); > if (ret < 0) > -- > git-series 0.8.11 > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
