Re: [PATCH 0/3] RFC: Add a drm_aux-dev module.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Sep 14, 2015 at 04:12:29PM -0700, Rafael Antognolli wrote:
> This is a tentative implementation of a module that allows reading/writing
> arbitrary dpcd registers, following the suggestion from Daniel Vetter. It
> assumes the drm aux helpers were used by the driver.
> 
> I tried to follow the i2c-dev implementation as close as possible, but the only
> operations that are provided on the dev node are two different ioctl's, one for
> reading a register and another one for writing it.

Why would you use ioctls instead of normal read/write syscalls?

> 
> I have at least 2 open questions:
> 
>  * Right now the AUX channels are stored in a global list inside the
>    drm_dp_helper implementation, and I assume that's not ideal. A different
>    approach would be to iterate over the list of connectors, instead of the
>    list of AUX channels, but that would require the struct drm_connector or
>    similar to know about the respective aux helper. It could be added as a
>    function to register that, or as a new method on the drm_connector_funcs to
>    retrieve the aux channel helper.
> 
>  * From the created sysfs drm_aux-dev device it's possible to know what is the
>    respective connector, but not the other way around. Is this good enough?
> 
> Please provide any feedback you have and tell me if this is the idea you had
> initially for this kind of implementation. Or, if it's nothing like this, let
> me know what else you had in mind.
> 
> If I'm going in the right direction, I'll refine the patch to provide full
> documentation and tests if needed.
> 
> Rafael Antognolli (3):
>   drm/dp: Keep a list of drm_dp_aux helper.
>   drm/dp: Store the drm_connector device pointer on the helper.
>   drm/dp: Add a drm_aux-dev module for reading/writing dpcd registers.
> 
>  Documentation/ioctl/ioctl-number.txt |   1 +
>  drivers/gpu/drm/Kconfig              |   4 +
>  drivers/gpu/drm/Makefile             |   1 +
>  drivers/gpu/drm/drm_aux-dev.c        | 390 +++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_dp_helper.c      |  71 +++++++
>  drivers/gpu/drm/i915/intel_dp.c      |   1 +
>  include/drm/drm_dp_helper.h          |   7 +
>  include/uapi/linux/Kbuild            |   1 +
>  include/uapi/linux/drm_aux-dev.h     |  45 ++++
>  9 files changed, 521 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_aux-dev.c
>  create mode 100644 include/uapi/linux/drm_aux-dev.h
> 
> -- 
> 2.4.0
> 
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-- 
Ville Syrjälä
Intel OTC
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