On Fri, Dec 8, 2023 at 12:00 AM Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > > On 12/7/23 17:10, Dragan Simic wrote: > > On 2023-12-07 10:25, Jensen Huang wrote: > >> On Thu, Dec 7, 2023 at 4:37 PM Dragan Simic <dsimic@xxxxxxxxxxx> wrote: > >>> > >>> On 2023-12-07 09:21, Jensen Huang wrote: > >>> > Possible deadlock scenario (on reboot): > >>> > rk3x_i2c_xfer_common(polling) > >>> > -> rk3x_i2c_wait_xfer_poll() > >>> > -> rk3x_i2c_irq(0, i2c); > >>> > --> spin_lock(&i2c->lock); > >>> > ... > >>> > <rk3x i2c interrupt> > >>> > -> rk3x_i2c_irq(0, i2c); > >>> > --> spin_lock(&i2c->lock); (deadlock here) > >>> > > >>> > Store the IRQ number and disable/enable it around the polling > >>> transfer. > >>> > This patch has been tested on NanoPC-T4. > >>> > >>> In case you haven't already seen the related discussion linked below, > >>> please have a look. I also added more people to the list of recipients, > >>> in an attempt to make everyone aware of the different approaches to > >>> solving this issue. > >>> > >>> https://lore.kernel.org/all/655177f4.050a0220.d85c9.3ba0@xxxxxxxxxxxxx/T/#m6fc9c214452fec6681843e7f455978c35c6f6c8b > >> > >> Thank you for providing the information. I hadn't seen this link before. > >> After carefully looking into the related discussion, it appears that > >> Dmitry Osipenko is already working on a suitable patch. To avoid > >> duplication > >> or conflicts, my patch can be discarded. > > > > Thank you for responding so quickly. Perhaps it would be best to hear > > from Dmitry as well, before discarding anything. It's been a while > > since Dmitry wrote about working on the patch, so he might have > > abandoned it. > > This patch is okay. In general, will be better to have IRQ disabled by > default like I did in my variant, it should allow to remove the spinlock > entirely. Of course this also can be done later on in a follow up > patches. Jensen, feel free to use my variant of the patch, add my > s-o-b+co-developed tags to the commit msg if you'll do. Otherwise I'll > be able to send my patch next week. Thank you for the suggestion. I've updated the patch to your variant, and as confirmed by others, reboots are functioning correctly. I measured the overhead of enable_irq/disable_irq() by calculating ktime in the updated version, and on rk3399, the minimum delta I observed was 291/875 ns. This extra cost may impact most interrupt-based transfers. Therefore, I personally lean towards the current v2 patch and handle the spinlock and irqsave/restore in a follow up patch. I'd like to hear everyone's thoughts on this. -- Best regards, Jensen
