Hi Tomi, Devarsh,
On 10/21/24 19:37, Tomi Valkeinen wrote:
It has been observed that sometimes DSS will trigger an interrupt and the top level interrupt (DISPC_IRQSTATUS) is not zero, but the VP and VID level interrupt-statuses are zero.
Does this mean that there was a legitimate interrupt that potentially went unrecognized? Or that there was a, for the lack of a better word, fake interrupt trigger that doesn't need handling but just clearing?
As the top level irqstatus is supposed to tell whether we have VP/VID interrupts, the thinking of the driver authors was that this particular case could never happen. Thus the driver only clears the DISPC_IRQSTATUS bits which has corresponding interrupts in VP/VID status. So when this issue happens, the driver will not clear DISPC_IRQSTATUS, and we get an interrupt flood.
It is unclear why the issue happens. It could be a race issue in the driver, but no such race has been found. It could also be an issue with the HW. However a similar case can be easily triggered by manually writing to DISPC_IRQSTATUS_RAW. This will forcibly set a bit in the DISPC_IRQSTATUS and trigger an interrupt, and as the driver never clears the bit, we get an interrupt flood.
To fix the issue, always clear DISPC_IRQSTATUS. The concern with this solution is that if the top level irqstatus is the one that triggers the interrupt, always clearing DISPC_IRQSTATUS might leave some interrupts unhandled if VP/VID interrupt statuses have bits set. However, testing shows that if any of the irqstatuses is set (i.e. even if DISPC_IRQSTATUS == 0, but a VID irqstatus has a bit set), we will get an interrupt.
Does this mean if VID/VP irqstatus has been set right around the time the equivalent DISPC_IRQSTATUS bit is being cleared, the equivalent DISPC_IRQSTATUS bit is going to get set again, and make the driver handle the event as we expect it to?
Signed-off-by: Tomi Valkeinen tomi.valkeinen@ideasonboard.com Co-developed-by: Bin Liu b-liu@ti.com Signed-off-by: Bin Liu b-liu@ti.com Co-developed-by: Devarsh Thakkar devarsht@ti.com Signed-off-by: Devarsh Thakkar devarsht@ti.com Co-developed-by: Jonathan Cormier jcormier@criticallink.com Signed-off-by: Jonathan Cormier jcormier@criticallink.com Fixes: 32a1795f57ee ("drm/tidss: New driver for TI Keystone platform Display SubSystem") Cc: stable@vger.kernel.org
drivers/gpu/drm/tidss/tidss_dispc.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c index 1ad711f8d2a8..f81111067578 100644 --- a/drivers/gpu/drm/tidss/tidss_dispc.c +++ b/drivers/gpu/drm/tidss/tidss_dispc.c @@ -780,24 +780,20 @@ static void dispc_k3_clear_irqstatus(struct dispc_device *dispc, dispc_irq_t clearmask) { unsigned int i;
- u32 top_clear = 0;
for (i = 0; i < dispc->feat->num_vps; ++i) {
if (clearmask & DSS_IRQ_VP_MASK(i)) {
if (clearmask & DSS_IRQ_VP_MASK(i)) dispc_k3_vp_write_irqstatus(dispc, i, clearmask);
top_clear |= BIT(i);}if (clearmask & DSS_IRQ_PLANE_MASK(i)) {
if (clearmask & DSS_IRQ_PLANE_MASK(i)) dispc_k3_vid_write_irqstatus(dispc, i, clearmask);
top_clear |= BIT(4 + i);}
nit: Maybe these for-loop braces could be dropped as well.
Otherwise, LGTM,
Reviewed-by: Aradhya Bhatia aradhya.bhatia@linux.dev
Regards Aradhya
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