For ATI GPU the crtc_base could be the base pointer to the memory buffer: ./drivers/gpu/drm/radeon/rv770.c: u32 rv770_page_flip(struct radeon_device *rdev, int crtc_id, u64 crtc_base) ./drivers/gpu/drm/radeon/rs600.c: void rs600_pre_page_flip(struct radeon_device *rdev, int crtc) void rs600_post_page_flip(struct radeon_device *rdev, int crtc) u32 rs600_page_flip(struct radeon_device *rdev, int crtc_id, u64 crtc_base) As to the internals of these buffer area, well, u may need the datasheet from the vendor. Just grep for "CRTC" inside the gpu/drm/radeon directory and you can understand why. On Thu, Jan 16, 2014 at 3:44 PM, Peter Teoh <htmldeveloper@gmail.com> wrote:

In general how it worked is explained here:

https://www.kernel.org/doc/htmldocs/drm/drm-kms-init.html

Not sure which is the name of your video card, but I think in general all the page flip API should have access to the scan buffer (see link above). For Intel these are possible APIs :

static void do_intel_finish_page_flip(struct drm_device *dev, void intel_finish_page_flip(struct drm_device *dev, int pipe) do_intel_finish_page_flip(dev, crtc); void intel_finish_page_flip_plane(struct drm_device *dev, int plane) do_intel_finish_page_flip(dev, crtc); void intel_prepare_page_flip(struct drm_device *dev, int plane) * is also accompanied by a spurious intel_prepare_page_flip(). inline static void intel_mark_page_flip_active(struct intel_crtc *intel_crtc)

On Sat, Jan 11, 2014 at 9:27 PM, Sannu K <sannumail4foss@gmail.com> wrote:

...

Hi,

I would like to access a monitor's content in kernel mode. I tried but could not find a generic way to access CRTC's scan out buffer in kernel mode. I prefer to do it in kernel mode as an experiment. Any pointers will greatly help.

Thanks and Regards, Sannu K

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-- Regards, Peter Teoh

-- Regards, Peter Teoh

As indicated here: http://www.botchco.com/agd5f/?p=51 the input to CRTC is the framebuffer, and output of CRTC is already monitor-level information...which is meaningless to you. So but best bet is to get it at the framebuffer level? Correct me if wrong? On Thu, Jan 16, 2014 at 8:06 PM, Sannu K <sannumail4foss@gmail.com> wrote:

On Thu, Jan 16, 2014 at 1:14 PM, Peter Teoh <htmldeveloper@gmail.com>wrote:

...

In general how it worked is explained here:

https://www.kernel.org/doc/htmldocs/drm/drm-kms-init.html

Not sure which is the name of your video card, but I think in general all the page flip API should have access to the scan buffer (see link above). For Intel these are possible APIs :

Thanks. I was trying to find out a generic way to access the scan out buffer. The page flip functions looks specific to hardware.

...

static void do_intel_finish_page_flip(struct drm_device *dev, void intel_finish_page_flip(struct drm_device *dev, int pipe) do_intel_finish_page_flip(dev, crtc); void intel_finish_page_flip_plane(struct drm_device *dev, int plane) do_intel_finish_page_flip(dev, crtc); void intel_prepare_page_flip(struct drm_device *dev, int plane) * is also accompanied by a spurious intel_prepare_page_flip(). inline static void intel_mark_page_flip_active(struct intel_crtc *intel_crtc)

-- Regards, Peter Teoh

It is enough to have a way to get the content of scan out buffer instead of accessing it directly using a pointer.

Thanks for you help, Sannu K

-- Regards, Peter Teoh