Re: [PATCH 3/4] drm: xlnx: zynqmp_dpsub: Don't generate vblank in live mode

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Anatoliy,

On Fri, Jan 19, 2024 at 05:53:30AM +0000, Klymenko, Anatoliy wrote:
> On Wed, 17 Jan 2024 16:20:10 +0200, Tomi Valkeinen wrote:
> > On 13/01/2024 01:42, Anatoliy Klymenko wrote:
> > > Filter out status register against interrupts' mask.
> > > Some events are being reported via DP status register, even if
> > > corresponding interrupts have been disabled. Avoid processing of such
> > > events in interrupt handler context.
> > 
> > The subject talks about vblank and live mode, the the description doesn't. Can
> > you elaborate in the desc a bit about when this is an issue and why it wasn't
> > before?
> 
> Yes, I should make patch comment more consistent and elaborate. I will fix it in the next version. Thank you.
> 
> > 
> > > Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@amd.com>
> > > ---
> > >   drivers/gpu/drm/xlnx/zynqmp_dp.c | 11 +++++++++--
> > >   1 file changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > index d60b7431603f..571c5dbc97e5 100644
> > > --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > @@ -1624,8 +1624,16 @@ static irqreturn_t zynqmp_dp_irq_handler(int irq, void *data)
> > >       u32 status, mask;
> > >
> > >       status = zynqmp_dp_read(dp, ZYNQMP_DP_INT_STATUS);
> > > +     zynqmp_dp_write(dp, ZYNQMP_DP_INT_STATUS, status);
> > >       mask = zynqmp_dp_read(dp, ZYNQMP_DP_INT_MASK);
> > > -     if (!(status & ~mask))
> > > +
> > > +     /*
> > > +      * Status register may report some events, which corresponding interrupts
> > > +      * have been disabled. Filter out those events against interrupts' mask.
> > > +      */
> > > +     status &= ~mask;
> > > +
> > > +     if (!status)
> > >               return IRQ_NONE;
> > >
> > >       /* dbg for diagnostic, but not much that the driver can do */
> > > @@ -1634,7 +1642,6 @@ static irqreturn_t zynqmp_dp_irq_handler(int irq, void *data)
> > >       if (status & ZYNQMP_DP_INT_CHBUF_OVERFLW_MASK)
> > >               dev_dbg_ratelimited(dp->dev, "overflow interrupt\n");
> > >
> > > -     zynqmp_dp_write(dp, ZYNQMP_DP_INT_STATUS, status);
> > >
> > >       if (status & ZYNQMP_DP_INT_VBLANK_START)
> > >               zynqmp_dpsub_drm_handle_vblank(dp->dpsub);
> > 
> > Moving the zynqmp_dp_write() is not related to this fix, is it? I think it should be in
> > a separate patch.
> 
> The sole purpose of zynqmp_dp_write() is to clear status register. The
> sooner we do it the better (after reading status in the local variable
> of course).

No disagreement about that. Tomi's point is that it's a good change, but
it should be done in a separate patch, by itself, not bundled with other
changes. The usual rule in the kernel is "one change, one commit".

> We can also reuse status variable for in-place filtering
> against the interrupt mask, which makes this change dependent on
> zynqmp_dp_write() reordering. I will add a comment explaining this. Is
> it ok?

-- 
Regards,

Laurent Pinchart