linux-kernel - Re: [PATCH 1/2] spi: Add call to spi_slave_abort() function when spidev driver is released

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Date:   Thu, 26 Sep 2019 09:59:41 +0200
From:   Lukasz Majewski <lukma@...x.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Mark Brown <broonie@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH 1/2] spi: Add call to spi_slave_abort() function when
 spidev driver is released

Hi Geert,

> Hi Lukasz,
> 
> On Thu, Sep 26, 2019 at 3:33 AM Lukasz Majewski <lukma@...x.de> wrote:
> > This change is necessary for spidev devices (e.g. /dev/spidev3.0)
> > working in the slave mode (like NXP's dspi driver for Vybrid SoC).
> >
> > When SPI HW works in this mode - the master is responsible for
> > providing CS and CLK signals. However, when some fault happens -
> > like for example distortion on SPI lines - the SPI Linux driver
> > needs a chance to recover from this abnormal situation and prepare
> > itself for next (correct) transmission.
> >
> > This change doesn't pose any threat on drivers working in master
> > mode as spi_slave_abort() function checks if SPI slave mode is
> > supported.
> >
> > Signed-off-by: Lukasz Majewski <lukma@...x.de>  
> 
> Thanks for your patch!
> 
> Yesterday I saw this appear on spi/for-next, but I couldn't find the
> email in my mbox.  Today it has arrived. Looks like gmail had some
> troubles ("Delivered after 138401 seconds", ugh).

I've already sent v2 of this patch, as Intel Linux test setup spot the
error with lack of #define guards.

> 
> > --- a/drivers/spi/spidev.c
> > +++ b/drivers/spi/spidev.c
> > @@ -627,6 +627,7 @@ static int spidev_release(struct inode *inode,
> > struct file *filp) if (dofree)
> >                         kfree(spidev);
> >         }
> > +       spi_slave_abort(spidev->spi);  
> 
> Looks good to me.  Just wondering if this should be done for the last
> user only, i.e. in the "if" block above, like resetting speed_hz?

I also thought about this. However, from my use case the user must end
the transmission with CTRL+C on his user space program, which in turn
communicate via SPI with /dev/spidev3.0.

There might be many (potential) programs using the /dev/spidev3.0 at the
same time, so the usage count may be not one.

For the above reason I've moved it outside the above if().

> 
> >         mutex_unlock(&device_list_lock);
> >
> >         return 0;  
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 




Best regards,

Lukasz Majewski

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