RE: [PATCH] spi: spi-rspi: Add force_dma variable to spi_ops

[Biju Das <biju.das.jz@xxxxxxxxxxxxxx>]

Hi Geert,

+Vinod

> Subject: Re: [PATCH] spi: spi-rspi: Add force_dma variable to spi_ops
> 
> Hi Biju,
> 
> On Tue, Jul 19, 2022 at 10:29 AM Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> wrote:
> > > Subject: Re: [PATCH] spi: spi-rspi: Add force_dma variable to
> > > spi_ops On Sat, Jul 16, 2022 at 5:39 PM Biju Das
> <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> > > > On RZ/G2L SoCs switching from DMA to interrupt mode, causes
> > > > timeout issue as we are not getting Rx interrupt even though SPRF
> > > > bit is set in the status register.
> > > >
> > > > But there is no issue if we don't switch between interrupt to DMA
> > > > mode or vice versa.
> > > >
> > > > Performance comparison between interrupt and DMA mode on RZ/Five
> > > > SMARC platform connected to a display module shows that
> > > > performance and CPU utilization is much better with DMA mode
> > > > compared to interrupt mode
> > > > (1->65 fps) and (98->8%).
> > > >
> > > > This patch introduces a variable force_dma to avoid switching
> > > > between DMA to interrupt mode for RZ platforms.
> > > >
> > > > Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> > >
> > > Thanks for your patch!
> > >
> > > > @@ -1196,6 +1197,7 @@ static const struct spi_ops rspi_rz_ops = {
> > > >         .flags =                SPI_CONTROLLER_MUST_RX |
> > > SPI_CONTROLLER_MUST_TX,
> > > >         .fifo_size =            8,      /* 8 for TX, 32 for RX */
> > > >         .num_hw_ss =            1,
> > > > +       .force_dma =            true,
> > > >  };
> > >
> > > Do you know if this is needed on RZ/A series, too?
> >
> > I guess it is needed?? I may be wrong. I got a link from Chris [1]. As
> > per this still We haven't found a solution. May be the priority is
> > changed for this activity and no one looked after this.
> >
> > [1]
> 
> Daniel said he found the issue, i.e. the dmac driver never resetting DMARS?

Currently DMARS set during prepare and it never cleared. So I added device_synchronize
callback in DMA driver to clear the DMARS. RSPI client driver after synchronizing
DMA callback, calls dmaengine_synchronize which clears DMARS.

With this DMA to interrupt mode switching is working fine.

Cheers,
Biju