Re: [RFC v4 16/20] drm/i915/dp: Extract drm_dp_get_sink_count()

Lyude Paul
2020-08-26T17:10:55Z

On Wed, 2020-08-26 at 10:05 +0300, Jani Nikula wrote:
> On Tue, 25 Aug 2020, Lyude Paul <lyude@redhat.com> wrote:
> > And of course, we'll also need to read the sink count from other drivers
> > as well if we're checking whether or not it's supported. So, let's
> > extract the code for this into another helper.
> >
> > v2:
> > * Fix drm_dp_dpcd_readb() ret check
> > * Add back comment and move back sink_count assignment in
> > intel_dp_get_dpcd()
> >
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > Reviewed-by: Sean Paul <sean@poorly.run>
> > ---
> > drivers/gpu/drm/drm_dp_helper.c | 22 ++++++++++++++++++++++
> > drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++------
> > include/drm/drm_dp_helper.h | 1 +
> > 3 files changed, 28 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_dp_helper.c
> > b/drivers/gpu/drm/drm_dp_helper.c
> > index 863e0babc1903..67ad05eb05b7e 100644
> > --- a/drivers/gpu/drm/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/drm_dp_helper.c
> > @@ -736,6 +736,28 @@ bool drm_dp_has_sink_count(struct drm_connector
> > *connector,
> > }
> > EXPORT_SYMBOL(drm_dp_has_sink_count);
> >
> > +/**
> > + * drm_dp_get_sink_count() - Retrieve the sink count for a given sink
>
> From the department of bikeshedding...
>
> Should we have a naming scheme where it's obvious whether a function
> will do DPCD access, or just shuffle existing data?
>
> For example, drm_dp_read_foo() for anything with DPCD access
> vs. drm_dp_get_foo() or even simpler for anything that only processes
> pre-read data?
>
> > + * @aux: The DP AUX channel to use
> > + *
> > + * Returns: The current sink count reported by @aux, or a negative error
> > code
> > + * otherwise.
> > + */
> > +int drm_dp_get_sink_count(struct drm_dp_aux *aux)
> > +{
> > + u8 count;
> > + int ret;
> > +
> > + ret = drm_dp_dpcd_readb(aux, DP_SINK_COUNT, &count);
> > + if (ret < 0)
> > + return ret;
> > + if (ret != 1)
> > + return -EIO;
>
> Makes me wonder if that shouldn't be at drm_dp_dpcd_read() level, for
> reads returning 0..len-1 bytes. Not necessarily part of this series, but
> seems silly to set a precedent to start handling that return value all
> over the place.
>
Yeah definitely - I'm probably going to keep this code here for now, but I would
like to convert drm_dp_dpcd_readb/writeb() to just return 0 on success (all
bytes written, I've never once seen a situation where we got less bytes than we
read - it's always all or nothing) and negative error code on failure. I'll get
to that soon

> BR,
> Jani.
>
> > +
> > + return DP_GET_SINK_COUNT(count);
> > +}
> > +EXPORT_SYMBOL(drm_dp_get_sink_count);
> > +
> > /*
> > * I2C-over-AUX implementation
> > */
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 35a4779a442e2..4337321a3be4f 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -4648,6 +4648,8 @@ intel_dp_has_sink_count(struct intel_dp *intel_dp)
> > static bool
> > intel_dp_get_dpcd(struct intel_dp *intel_dp)
> > {
> > + int ret;
> > +
> > if (!intel_dp_read_dpcd(intel_dp))
> > return false;
> >
> > @@ -4664,11 +4666,8 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> > }
> >
> > if (intel_dp_has_sink_count(intel_dp)) {
> > - u8 count;
> > - ssize_t r;
> > -
> > - r = drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_COUNT, &count);
> > - if (r < 1)
> > + ret = drm_dp_get_sink_count(&intel_dp->aux);
> > + if (ret < 0)
> > return false;
> >
> > /*
> > @@ -4676,7 +4675,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
> > * a member variable in intel_dp will track any changes
> > * between short pulse interrupts.
> > */
> > - intel_dp->sink_count = DP_GET_SINK_COUNT(count);
> > + intel_dp->sink_count = ret;
> >
> > /*
> > * SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
> > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> > index a1413a531eaf4..0c141fc81aaa8 100644
> > --- a/include/drm/drm_dp_helper.h
> > +++ b/include/drm/drm_dp_helper.h
> > @@ -1635,6 +1635,7 @@ struct drm_dp_desc;
> > bool drm_dp_has_sink_count(struct drm_connector *connector,
> > const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> > const struct drm_dp_desc *desc);
> > +int drm_dp_get_sink_count(struct drm_dp_aux *aux);
> >
> > void drm_dp_remote_aux_init(struct drm_dp_aux *aux);
> > void drm_dp_aux_init(struct drm_dp_aux *aux);
--
Sincerely,
Lyude Paul (she/her)
Software Engineer at Red Hat