On Tue, Nov 17, 2020 at 12:56:44PM +0200, Andy Shevchenko wrote:
> On Tue, Nov 17, 2020 at 11:45 AM Serge Semin
> <sergey.se...@baikalelectronics.ru> wrote:
> >
> > I've discovered that due to the recent commit 49d7d695ca4b ("spi: dw:
> > Explicitly de-assert CS on SPI transfer completion") a concurrent usage of
> > the spidev devices with different chip-selects causes the "SPI transfer
> > timed out" error.
>
> I'll read this later...
>
> > + mutex_lock(&spi->controller->io_mutex);
> > +
> > if (spi->controller->setup)
> > status = spi->controller->setup(spi);
> >
> > if (spi->controller->auto_runtime_pm && spi->controller->set_cs) {
> > status = pm_runtime_get_sync(spi->controller->dev.parent);
>
> I didn't check what this lock is protecting,
It is used to protect the SPI io operations. So it's locked only
during the SPI memory operations and the SPI-message execution. That's
the time when the core toggles the controller chip-selects by calling
the spi_set_cs() method and the set_cs callback.
> but have you checked all
> PM runtime callbacks if they are not taking the lock. When you call PM
> runtime functions with 'sync' it may include a lot of work, some of
> which may sleep (not a problem for mutex) and may take arbitrary locks
> (might be a deadlock in case of trying the same lock).
Yeah, I understand that. Simple grepping hasn't showed anyone else but
the SPI-core using it. So unless the controllers PM methods also call
spi_setup() or request SPI-transfers, there shouldn't be a deadlock.
Moreover as I can see from the __spi_pump_messages() method the
IO-mutex is locked during the sync-suffixed PM-methods invocation.
AFAICS locking io_mutex around the PM-methods here shouldn't cause
problems. But of course testing it in various platforms/controllers is
always welcome.
-Sergey
>
> > if (status < 0) {
> > + mutex_unlock(&spi->controller->io_mutex);
> > pm_runtime_put_noidle(spi->controller->dev.parent);
> > dev_err(&spi->controller->dev, "Failed to power
> > device: %d\n",
> > status);
> > @@ -3354,6 +3357,8 @@ int spi_setup(struct spi_device *spi)
> > spi_set_cs(spi, false);
> > }
> >
> > + mutex_unlock(&spi->controller->io_mutex);
> > +
>
>
> --
> With Best Regards,
> Andy Shevchenko
