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@xxxxxxxxx> 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@xxxxxxxxx>
>
> 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
