On 3/20/24 02:53, Tomi Valkeinen wrote:
On 20/03/2024 00:51, Sean Anderson wrote:
Retraining the link can take a while, and might involve waiting for
DPCD reads/writes to complete. This is inappropriate for an IRQ handler.
Just schedule this work for later completion. This is racy, but will be
fixed in the next commit.
You should add the locks first, and use them here, rather than first
adding a buggy commit and fixing it in the next one.
I didn't think I could add the locks first since I only noticed the IRQ
was threaded right before sending out this series. So yeah, we could add
locking, add the workqueue, and then unthread the IRQ.
Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
---
Actually, on second look this IRQ is threaded. So why do we have a
workqueue for HPD events? Maybe we should make it unthreaded?
Indeed, there's not much work being done in the IRQ handler. I don't know why it's threaded.
We could move the queued work to be inside the threaded irq handler,
but with a quick look, the HPD work has lines like "msleep(100)" (and
that's inside a for loop...), which is probably not a good thing to do
even in threaded irq handler.
Although I'm not sure if that code is good to have anywhere. Why do we
even have such code in the HPD work path... We already got the HPD
interrupt. What does "It takes some delay (ex, 100 ~ 500 msec) to get
the HPD signal with some monitors" even mean...
The documentation for this bit is
| HPD_STATE 0 ro 0x0 Contains the raw state of the HPD pin on the DisplayPort connector.
So I think the idea is to perform some debouncing.
Would it be possible to clean up the work funcs a bit (I haven't
looked a the new work func yet), to remove the worst extra sleeps, and
just do all that inside the threaded irq handler?
Probably not, since a HPD IRQ results in link retraining, which can take a while.
Do we need to handle interrupts while either delayed work is being done?
Probably not.
If we do need a delayed work, would just one work be enough which
handles both HPD_EVENT and HPD_IRQ, instead of two?
Maybe, but then we need to determine which pending events we need to
handle. I think since we have only two events it will be easier to just
have separate workqueues.