Hi,
On Tue, Mar 12, 2024 at 5:47 PM Guenter Roeck <groeck@xxxxxxxxxx> wrote:
>
> On Tue, Mar 12, 2024 at 5:14 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
> >
> > As documented in the description of the transfer() function of
> > "struct drm_dp_aux", the transfer() function can be called at any time
> > regardless of the state of the DP port. Specifically if the kernel has
> > the DP AUX character device enabled and userspace accesses
> > "/dev/drm_dp_auxN" directly then the AUX transfer function will be
> > called regardless of whether a DP device is connected.
> >
> > For eDP panels we have a special rule where we wait (with a 5 second
> > timeout) for HPD to go high. This rule was important before all panels
> > drivers were converted to call wait_hpd_asserted() and actually can be
> > removed in a future commit.
> >
> > For external DP devices we never checked for HPD. That means that
> > trying to access the DP AUX character device (AKA `hexdump -C
> > /dev/drm_dp_auxN`) would very, very slowly timeout. Specifically on my
> > system:
> > $ time hexdump -C /dev/drm_dp_aux0
> > hexdump: /dev/drm_dp_aux0: Connection timed out
> >
> > real 0m8.200s
> >
> > Let's add a check for HPD to avoid the slow timeout. This matches
> > what, for instance, the intel_dp_aux_xfer() function does when it
> > calls intel_tc_port_connected_locked(). That call has a document by it
> > explaining that it's important to avoid the long timeouts.
> >
> > Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support")
> > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> > ---
> >
> > drivers/gpu/drm/msm/dp/dp_aux.c | 8 +++++++-
> > drivers/gpu/drm/msm/dp/dp_catalog.c | 10 ++++++++++
> > drivers/gpu/drm/msm/dp/dp_catalog.h | 1 +
> > 3 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c b/drivers/gpu/drm/msm/dp/dp_aux.c
> > index 03f4951c49f4..de0b0eabced9 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_aux.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
> > @@ -307,7 +307,8 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux *dp_aux,
> > * turned on the panel and then tried to do an AUX transfer. The panel
> > * driver has no way of knowing when the panel is ready, so it's up
> > * to us to wait. For DP we never get into this situation so let's
> > - * avoid ever doing the extra long wait for DP.
> > + * avoid ever doing the extra long wait for DP and just query HPD
> > + * directly.
> > */
> > if (aux->is_edp) {
> > ret = dp_catalog_aux_wait_for_hpd_connect_state(aux->catalog);
> > @@ -315,6 +316,11 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux *dp_aux,
> > DRM_DEBUG_DP("Panel not ready for aux transactions\n");
> > goto exit;
> > }
> > + } else {
> > + if (!dp_catalog_aux_is_hpd_connected(aux->catalog)) {
> > + ret = -ENXIO;
> > + goto exit;
> > + }
> > }
> >
> > dp_aux_update_offset_and_segment(aux, msg);
> > diff --git a/drivers/gpu/drm/msm/dp/dp_catalog.c b/drivers/gpu/drm/msm/dp/dp_catalog.c
> > index 5142aeb705a4..93e2d413a1e7 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_catalog.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_catalog.c
> > @@ -266,6 +266,16 @@ int dp_catalog_aux_wait_for_hpd_connect_state(struct dp_catalog *dp_catalog)
> > 2000, 500000);
> > }
> >
> > +bool dp_catalog_aux_is_hpd_connected(struct dp_catalog *dp_catalog)
> > +{
> > + struct dp_catalog_private *catalog = container_of(dp_catalog,
> > + struct dp_catalog_private, dp_catalog);
> > +
> > + /* poll for hpd connected status every 2ms and timeout after 500ms */
>
> Maybe I am missing something, but the comment doesn't seem to match
> the code below.
>
> Guenter
>
> > + return readl(catalog->io->dp_controller.aux.base + REG_DP_DP_HPD_INT_STATUS) &
> > + DP_DP_HPD_STATE_STATUS_CONNECTED;
LOL. I guess I overlooked that. Thanks for catching! The comment got
copied from the dp_catalog_aux_wait_for_hpd_connect_state(). I'll
remove the comment and send a v2, but I'll wait a little bit to see if
there is additional feedback.
-Doug
