[Intel-gfx] [PATCH v3] drm/i915: Add debugfs to read/write any DPCD register

[Daniel Vetter]

On Mon, Apr 20, 2015 at 05:08:14PM +0530, Durgadoss R wrote:
> This patch creates a connector specific debugfs
> interface to read any particular DPCD register.
> The DPCD register address (hex format) is written
> to 'i915_dpcd_addr' interface and the corresponding
> value can be read from 'i915_dpcd_val' interface.
> 
> To write into a DPCD register, echo a value into
> 'i915_dpcd_val' interface. This will return -EIO
> for invalid writes.
> 
> Example usage:
> echo 0x2 > i915_dpcd_addr
> cat i915_dpcd_val
> 0x84
> 
> To write 0x1 to DPCD 0x170:
> echo 0x170 > i915_dpcd_addr
> echo 0x1 > i915_dpcd_val
> cat i915_dpcd_val
> 0x1
> 
> v2: Address Jani's comments.
> 
> v3: Added capability to write DPCD also (Ville)
> 
> Signed-off-by: Durgadoss R <durgadoss.r at intel.com>

As mentioned in another thread I think the right approach here is to
expose the dp aux interface through some ioctls in debugfs or dev
somewhere, and then add simple tools on top of that. Similar to what we
have with i2c. That would allow us to implement additional things on top
like mst inspection or using the i2c-over-dp-aux sidechannel.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch