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 [off-list ref] 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 [off-list ref] wrote:

quoted

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

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Regards,
Peter Teoh
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