Re: [PATCH 1/5] spi: Fix controller unregister order

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Fri, May 15, 2020 at 7:41 PM Lukas Wunner <lukas@xxxxxxxxx> wrote:
>
> On Fri, May 15, 2020 at 05:27:25PM +0100, Mark Brown wrote:
> > On Fri, May 15, 2020 at 05:58:01PM +0200, Lukas Wunner wrote:
> > > However since commit ffbbdd21329f ("spi: create a message queueing
> > > infrastructure"), spi_destroy_queue() is executed before unbinding the
> > > slaves.  It sets ctlr->running = false, thereby preventing SPI bus
> > > access and causing unbinding of slave devices to fail.
> >
> > Devices should basically never fail an unbind operation - if something
> > went seriously wrong there's basically nothing that can be done in terms
> > of error handling and keeping the device around isn't going to help.
>
> I guess the word "fail" in the commit message invites misinterpretations.
> The driver does unbind from the slave device, but the physical device is
> not left in a proper state.  E.g. interrupts may still be generated by
> the device because writing a register to disable them failed.

I didn't check a patch, but I see a bug on kernel bugzilla against
spi-pxa2xx because of this. It requires quite untrivial ->remove() in
order to quiescent the DMA and other activities.

-- 
With Best Regards,
Andy Shevchenko