Hi Łukasz,
On 1/21/25 11:28 AM, Łukasz Czechowski wrote:
Hi Quentin,
On 1/21/25 10:41 AM, Quentin Schulz <quentin.schulz@xxxxxxxxx> wrote:
Hi Lukasz,
On 1/21/25 10:22 AM, Lukasz Czechowski wrote:
UART controllers without flow control seem to behave unstable
in case DMA is enabled. The issues were indicated in the message:
https://lore.kernel.org/linux-arm-kernel/CAMdYzYpXtMocCtCpZLU_xuWmOp2Ja_v0Aj0e6YFNRA-yV7u14g@xxxxxxxxxxxxxx/
In case of PX30-uQ7 Ringneck SoM, it was noticed that after couple
of hours of UART communication, the CPU stall was occurring,
leading to the system becoming unresponsive.
After disabling the DMA, extensive UART communication tests for
up to two weeks were performed, and no issues were further
observed.
The flow control pins for uart5 are not available on PX30-uQ7
Ringneck, as configured by pinctrl-0, so the DMA nodes were
removed on SoM dtsi.
Reviewed-by: Quentin Schulz <quentin.schulz@xxxxxxxxx>
We should backport this to stable releases too, so please follow the
instructions from here:
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#select-the-recipients-for-your-patch
Essentially:
Cc: stable@xxxxxxxxxxxxxxx
in the commit log and we'll need a
Fixes: <commit hash>
trailer as well with the commit hash of the commit introducing the issue
(likely the one defining uart5 for Ringneck for us).
Considering that UART0 CTS and RTS are routed to Q7 header but only
usable when Haikou exposes UART0 on the DB9 connector (via the SW2
switch), which is NOT the default state (and in any case not supported
by our current device tree), I believe we should make the same change to
the uart0 node in haikou dts for Ringneck. What do you think? Can you
send another patch for that one?
It seems that in case of uart0, that is configured as kernel console, the DMA
is not used by the kernel:
https://lore.kernel.org/linux-serial/20200217114016.49856-7-andriy.shevchenko@xxxxxxxxxxxxxxx/
Which is likely why the issue was not observed so far. However it might be
good to do the same change to be on the safe side.
Should I extend this patch series with the fix for the Haikou device tree then,
or create a new one?
Ah, I had missed that one, thanks for the heads up. Just a small remark,
better send links to merged commits rather than mailing list patches,
it's a bit more difficult to figure out if the patch (and that version
of the patch) is merged. If there was an interesting discussion on the
patch and that information got lost when merging, nice to add the ML
link though!
In the case of the linked patch, it is merged indeed:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/tty/serial/8250/8250_port.c?id=089b6d36549160b535e109cd07ed6d578b81de46
No, no need to send a patch. When Haikou is configured to have UART0 on
the DB9 connector (and the Device Tree is adapted for it) and not use it
as kernel console, we should be able to use hardware flow control and
not have this issue. So we don't need to remove dmas/dma-names when it's
used as kernel console, and we don't need to remove them when routed to
DB9 connector either, so all good :)
Cheers,
Quentin
