Re: [PATCH] dmaengine: add verification of DMA_INTERRUPT capability for dmatest

Re: [PATCH] dmaengine: add verification of DMA_INTERRUPT capability for dmatest

[Geert Uytterhoeven]

Hi Dave, Vinod,

On Wed, Apr 13, 2022 at 12:58 AM Dave Jiang <dave.jiang@intel.com> wrote:
> Looks like I forgot to add DMA_INTERRUPT cap setting to the idxd driver and
> dmatest is still working regardless of this mistake. Add an explicit check
> of DMA_INTERRUPT capability for dmatest to make sure the DMA device being used
> actually supports interrupt before the test is launched and also that the
> driver is programmed correctly.
>
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Thanks for your patch, which is now commit a8facc7b988599f8
("dmaengine: add verification of DMA_INTERRUPT capability for
dmatest") upstream.

> --- a/drivers/dma/dmatest.c
> +++ b/drivers/dma/dmatest.c
> @@ -675,10 +675,16 @@ static int dmatest_func(void *data)
>         /*
>          * src and dst buffers are freed by ourselves below
>          */
> -       if (params->polled)
> +       if (params->polled) {
>                 flags = DMA_CTRL_ACK;
> -       else
> -               flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
> +       } else {
> +               if (dma_has_cap(DMA_INTERRUPT, dev->cap_mask)) {
> +                       flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
> +               } else {
> +                       pr_err("Channel does not support interrupt!\n");
> +                       goto err_pq_array;
> +               }
> +       }
>
>         ktime = ktime_get();
>         while (!(kthread_should_stop() ||
> @@ -906,6 +912,7 @@ static int dmatest_func(void *data)

Shimoda-san reports that this commit breaks dmatest on rcar-dmac.
Like most DMA engine drivers, rcar-dmac does not set the DMA_INTERRUPT
capability flag, hence dmatest now fails to start:

    dmatest: Channel does not support interrupt!

To me, it looks like the new check is bogus, as I believe it confuses
two different concepts:

  1. Documentation/driver-api/dmaengine/provider.rst says:

       - DMA_INTERRUPT

         - The device is able to trigger a dummy transfer that will
           generate periodic interrupts

  2. In non-polled mode, dmatest sets DMA_PREP_INTERRUPT.
     include/linux/dmaengine.h says:

       * @DMA_PREP_INTERRUPT - trigger an interrupt (callback) upon
completion of
       *  this transaction

As dmatest uses real transfers, I think it does not depend on
the ability to use interrupts from dummy transfers.

Do you agree?
Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] dmaengine: add verification of DMA_INTERRUPT capability for dmatest

[Vinod Koul]

On 30-05-22, 10:06, Geert Uytterhoeven wrote:
> Hi Dave, Vinod,

Hi Geert,

> 
> On Wed, Apr 13, 2022 at 12:58 AM Dave Jiang <dave.jiang@intel.com> wrote:
> > Looks like I forgot to add DMA_INTERRUPT cap setting to the idxd driver and
> > dmatest is still working regardless of this mistake. Add an explicit check
> > of DMA_INTERRUPT capability for dmatest to make sure the DMA device being used
> > actually supports interrupt before the test is launched and also that the
> > driver is programmed correctly.
> >
> > Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> 
> Thanks for your patch, which is now commit a8facc7b988599f8
> ("dmaengine: add verification of DMA_INTERRUPT capability for
> dmatest") upstream.
> 
> > --- a/drivers/dma/dmatest.c
> > +++ b/drivers/dma/dmatest.c
> > @@ -675,10 +675,16 @@ static int dmatest_func(void *data)
> >         /*
> >          * src and dst buffers are freed by ourselves below
> >          */
> > -       if (params->polled)
> > +       if (params->polled) {
> >                 flags = DMA_CTRL_ACK;
> > -       else
> > -               flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
> > +       } else {
> > +               if (dma_has_cap(DMA_INTERRUPT, dev->cap_mask)) {
> > +                       flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
> > +               } else {
> > +                       pr_err("Channel does not support interrupt!\n");
> > +                       goto err_pq_array;
> > +               }
> > +       }
> >
> >         ktime = ktime_get();
> >         while (!(kthread_should_stop() ||
> > @@ -906,6 +912,7 @@ static int dmatest_func(void *data)
> 
> Shimoda-san reports that this commit breaks dmatest on rcar-dmac.
> Like most DMA engine drivers, rcar-dmac does not set the DMA_INTERRUPT
> capability flag, hence dmatest now fails to start:
> 
>     dmatest: Channel does not support interrupt!
> 
> To me, it looks like the new check is bogus, as I believe it confuses
> two different concepts:
> 
>   1. Documentation/driver-api/dmaengine/provider.rst says:
> 
>        - DMA_INTERRUPT
> 
>          - The device is able to trigger a dummy transfer that will
>            generate periodic interrupts
> 
>   2. In non-polled mode, dmatest sets DMA_PREP_INTERRUPT.
>      include/linux/dmaengine.h says:
> 
>        * @DMA_PREP_INTERRUPT - trigger an interrupt (callback) upon
> completion of
>        *  this transaction
> 
> As dmatest uses real transfers, I think it does not depend on
> the ability to use interrupts from dummy transfers.

Yes this does not look right to me. DMA_INTERRUPT is for a specific
capability which is linked to dma_prep_interrupt() which dmatest does
not use so i think it is not correct for dmatest to use this...

I can revert this patch... Dave?

-- 
~Vinod

Re: [PATCH] dmaengine: add verification of DMA_INTERRUPT capability for dmatest

[Dave Jiang]

On 5/30/2022 10:24 PM, Vinod Koul wrote:
> On 30-05-22, 10:06, Geert Uytterhoeven wrote:
>> Hi Dave, Vinod,
> Hi Geert,
>
>> On Wed, Apr 13, 2022 at 12:58 AM Dave Jiang <dave.jiang@intel.com> wrote:
>>> Looks like I forgot to add DMA_INTERRUPT cap setting to the idxd driver and
>>> dmatest is still working regardless of this mistake. Add an explicit check
>>> of DMA_INTERRUPT capability for dmatest to make sure the DMA device being used
>>> actually supports interrupt before the test is launched and also that the
>>> driver is programmed correctly.
>>>
>>> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
>> Thanks for your patch, which is now commit a8facc7b988599f8
>> ("dmaengine: add verification of DMA_INTERRUPT capability for
>> dmatest") upstream.
>>
>>> --- a/drivers/dma/dmatest.c
>>> +++ b/drivers/dma/dmatest.c
>>> @@ -675,10 +675,16 @@ static int dmatest_func(void *data)
>>>          /*
>>>           * src and dst buffers are freed by ourselves below
>>>           */
>>> -       if (params->polled)
>>> +       if (params->polled) {
>>>                  flags = DMA_CTRL_ACK;
>>> -       else
>>> -               flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
>>> +       } else {
>>> +               if (dma_has_cap(DMA_INTERRUPT, dev->cap_mask)) {
>>> +                       flags = DMA_CTRL_ACK | DMA_PREP_INTERRUPT;
>>> +               } else {
>>> +                       pr_err("Channel does not support interrupt!\n");
>>> +                       goto err_pq_array;
>>> +               }
>>> +       }
>>>
>>>          ktime = ktime_get();
>>>          while (!(kthread_should_stop() ||
>>> @@ -906,6 +912,7 @@ static int dmatest_func(void *data)
>> Shimoda-san reports that this commit breaks dmatest on rcar-dmac.
>> Like most DMA engine drivers, rcar-dmac does not set the DMA_INTERRUPT
>> capability flag, hence dmatest now fails to start:
>>
>>      dmatest: Channel does not support interrupt!
>>
>> To me, it looks like the new check is bogus, as I believe it confuses
>> two different concepts:
>>
>>    1. Documentation/driver-api/dmaengine/provider.rst says:
>>
>>         - DMA_INTERRUPT
>>
>>           - The device is able to trigger a dummy transfer that will
>>             generate periodic interrupts
>>
>>    2. In non-polled mode, dmatest sets DMA_PREP_INTERRUPT.
>>       include/linux/dmaengine.h says:
>>
>>         * @DMA_PREP_INTERRUPT - trigger an interrupt (callback) upon
>> completion of
>>         *  this transaction
>>
>> As dmatest uses real transfers, I think it does not depend on
>> the ability to use interrupts from dummy transfers.
> Yes this does not look right to me. DMA_INTERRUPT is for a specific
> capability which is linked to dma_prep_interrupt() which dmatest does
> not use so i think it is not correct for dmatest to use this...
>
> I can revert this patch... Dave?
Yes we can revert it.