[PATCH] UPSTREAM: drm/amd/display: Fix Apple dongle cannot be successfully detected

[Louis Li]

On Mon, Oct 21, 2019 at 08:45:18PM +0800, Kazlauskas, Nicholas wrote:
> On 2019-10-21 3:54 a.m., Louis Li wrote:
> > [Why]
> > External monitor cannot be displayed consistently, if connecting
> > via this Apple dongle (A1621, USB Type-C to HDMI).
> > By experiments, it is confirmed that the dongle needs 200ms at least
> > to be ready for communication, after it sets HPD signal high.
> > 
> > [How]
> > When receiving HPD IRQ, delay 500ms at the beginning of handle_hpd_irq().
> > Then run the original procedure.
> > With this patch applied, the problem cannot be reproduced.
> > With other dongles, test results are PASS.
> > Test result is PASS after system resumes from suspend.
> > 
> > Signed-off-by: Louis Li <Ching-shih.Li at amd.com>
> > ---
> >   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > index 0aef92b7c037..043ddac73862 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -1025,6 +1025,11 @@ static void handle_hpd_irq(void *param)
> >   	struct drm_device *dev = connector->dev;
> >   	enum dc_connection_type new_connection_type = dc_connection_none;
> >   
> > +    /* Some monitors/dongles need around 200ms to be ready for communication
> > +     * after they drive HPD signal high.
> > +     */
> > +    mdelay(500);
> > +
> This sounds more like a quirk than behavior we want for all monitors, 
> but regardless this sleep isn't the correct place for this - since this 
> is an high priority interrupt handler this is really just blocking 
> everything for half a second.
> 
> I think it'd make more sense to queue off the work to occur half a 
> second later.
> 
> Nicholas Kazlauskas
> 

Yes, I agree with your comments. However, dealing with monitors and
dongles, it is proved that some monitors/dongles don't work as the
way people expected. The solution makes sense to have our driver
better compatibility to work with such devices. Truly, should not
block high priority interrupt. I had V2 patch to use msleep
instead. Customer is verifying V2. Will submit once it pass tests.

Louis Li

> >   	/* In case of failure or MST no need to update connector status or notify the OS
> >   	 * since (for MST case) MST does this in it's own context.
> >   	 */
> > 
>