Re: [Intel-gfx] [PATCH 1/2] drm/dp: Export drm_dp_dpcd_access()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 07 Apr 2022, Imre Deak <imre.deak@intel.com> wrote:
> The next patch needs a way to read a DPCD register without the preceding
> wake-up read in drm_dp_dpcd_read(). Export drm_dp_dpcd_access() to allow
> this.

I think I'd rather you added a special "probe" function for this
specific purpose. I think drm_dp_dpcd_access() is a too generic low
level function to export, and runs the risk of complicating any
potential future refactoring of the DP AUX code.

Something like this:

ssize_t drm_dp_dpcd_probe(struct drm_dp_aux *aux, unsigned int offset);

And you could reuse that for the wakeup in drm_dp_dpcd_read() too.


BR,
Jani.

>
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/dp/drm_dp.c    | 19 +++++++++++++++++--
>  include/drm/dp/drm_dp_helper.h |  2 ++
>  2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/dp/drm_dp.c b/drivers/gpu/drm/dp/drm_dp.c
> index 580016a1b9eb7..8b181314edcbe 100644
> --- a/drivers/gpu/drm/dp/drm_dp.c
> +++ b/drivers/gpu/drm/dp/drm_dp.c
> @@ -470,8 +470,22 @@ drm_dp_dump_access(const struct drm_dp_aux *aux,
>   * Both native and I2C-over-AUX transactions are supported.
>   */
>  
> -static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
> -			      unsigned int offset, void *buffer, size_t size)
> +/**
> + * drm_dp_dpcd_access() - read or write a series of bytes from/to the DPCD
> + * @aux: DisplayPort AUX channel (SST)
> + * @request: DP_AUX_NATIVE_READ or DP_AUX_NATIVE_WRITE
> + * @offset: address of the (first) register to read or write
> + * @buffer: buffer with the register values to write or the register values read
> + * @size: number of bytes in @buffer
> + *
> + * Returns the number of bytes transferred on success, or a negative error
> + * code on failure. This is a low-level function only for SST sinks and cases
> + * where calling drm_dp_dpcd_read()/write() is not possible (for instance due
> + * to the wake-up register read in drm_dp_dpcd_read()). For all other cases
> + * the latter functions should be used.
> + */
> +int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
> +		       unsigned int offset, void *buffer, size_t size)
>  {
>  	struct drm_dp_aux_msg msg;
>  	unsigned int retry, native_reply;
> @@ -526,6 +540,7 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
>  	mutex_unlock(&aux->hw_mutex);
>  	return ret;
>  }
> +EXPORT_SYMBOL(drm_dp_dpcd_access);
>  
>  /**
>   * drm_dp_dpcd_read() - read a series of bytes from the DPCD
> diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h
> index 1eccd97419436..7cf6e83434a8c 100644
> --- a/include/drm/dp/drm_dp_helper.h
> +++ b/include/drm/dp/drm_dp_helper.h
> @@ -2053,6 +2053,8 @@ struct drm_dp_aux {
>  	bool is_remote;
>  };
>  
> +int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
> +		       unsigned int offset, void *buffer, size_t size);
>  ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
>  			 void *buffer, size_t size);
>  ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,

-- 
Jani Nikula, Intel Open Source Graphics Center