On 29.08.23 16:35, Jagan Teki wrote:
On Sun, Aug 27, 2023 at 12:03 AM Mimoja <mimoja@xxxxxxxxx> wrote:
I appreciate you taking the time to respond!
On 26.08.23 17:18, Marek Vasut wrote:
On 8/26/23 11:55, Mimoja wrote:
"The .prepare() function is typically called before the display
controller
starts to transmit video data."
and
"After the display controller has started transmitting video data,
it's safe
to call the .enable() function."
DSI commands are not DSI video, so this should be OK ?
You are correct, my commit message is mixing things up here. I wanted to
emphasize roughly the thought of
"when enable() is called the dsi core is expected to have its clock
initialized". Will take note to clarify this if I succeed to
make a case for this patch below :)
While generally fine this can lead to a fillup of the transmission
queue before
the transmission is set up on certain dsi bridges.
This issue can also be seen on downstream imx8m* kernels.
Can you reproduce this with current mainline Linux or linux-next tree ?
I recall the display pipeline in the NXP downstream stuff is very
different from mainline .
You are very much correct. The NXP downstream kernel is completely
different from the upstream one
and is really a great example to show the issue (code cleaned up for
readability):
https://github.com/varigit/linux-imx/blob/5.15-2.0.x-imx_var01/drivers/gpu/drm/bridge/sec-dsim.c#L1368
```
ret = drm_panel_prepare(dsim->panel);
if (unlikely(ret)) [...]
/* config esc clock, byte clock and etc */
sec_mipi_dsim_config_clkctrl(dsim);
ret = drm_panel_enable(dsim->panel);
if (unlikely(ret)) [...]
```
Which SoC does have this problem ?
Sadly I don't have any SoCs available which would work perfectly with
linux-next, let alone are confirmed affected :/
I were able to make my Kingway Panel work (Custom one and so far
unsupported by the st7701 driver) with this
patch on downstream 5.4 and 5.15 imx8mn as well as on a raspberry pi CM4
with 6.1. However raspberrypi/linux brings
SPI support to the st7701 driver which should not affect this but I
would just like to document it here.
I could not find any success story with st7701 and the rpi on 6.1 online
after a short search (and only one
reference with 5.10 which seems to me a bit different in a short
comparison) but again I can only offer
circumstantial evidence. Sorry :/
If I understand correctly, 5.10 and 5.15 Would work as it is if the
DSI host calls the panel's prepare and enable directly from encoder
enable. Did you check that?
No, I fear the downstream NXP driver is not following the correct /
expected calling flow
which upstream has implemented. After investigating this and the RPi
issue I would like to
follow Marek's recommendation and simply sunset this change in favor of
fixing the
downstream issues in the downstream tree(s).
This seems to be mainly an issue for vendor-custom downstream host
kernels, and while there might be
a case of convention where panels don't sent commands in prepare() and
only in enable()
I don't think this patch should have a future solely to be cherry-picked
into downstream kernels,
when we can not make a case for current linux/next. After all: It is now
on the internet for better
or worse for others to pick up if needed.
I appreciate you all taking the time to discuss and I will post the
enablement code
for the Kingway HW-021P0Z002-01 panel I tested this with in a bit.
Cheers and thankful regards
Mimoja
