[PATCH 1/2] drm/dp: Export drm_dp_dpcd_access()

[Imre Deak]

On Thu, Apr 07, 2022 at 10:32:11PM +0300, Jani Nikula wrote:
> On Thu, 07 Apr 2022, Imre Deak <imre.deak at 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.

Ok, makes sense, I'll change that.

> BR,
> Jani.
> 
> >
> > Cc: dri-devel at lists.freedesktop.org
> > Signed-off-by: Imre Deak <imre.deak at 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