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

[Vinod Koul <vkoul@kernel.org>]

On 19-07-22, 11:28, Biju Das wrote:
> 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@bp.renesas.com>
> > 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@bp.renesas.com> 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.

Why do you need a variable for that, if DMA is availble (you were able
to allocate channels) then use DMA, otherwise fall back to PIO..

Or anything missing from context which I am not aware of?

> > > > >
> > > > > Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > >
> > > > 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
> 

-- 
~Vinod