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

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

Hi Geert,

+ Chris,

> Subject: Re: [PATCH] spi: spi-rspi: Add force_dma variable to spi_ops
> 
> Hi Biju,
> 
> 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] https://lore.kernel.org/linux-renesas-soc/?q=spi-rspi+mixes+DMA+and+PIO+transfers+causing+PIO+transfer+to+fail

> I knowupstream does not have DMA support for RZ/A yet, but the BSP has?

RZ/G2L DMA driver is derived from RZ/A, with small changes it can support RZ/A.
I am not sure is there any plan to upstream DMA support for RZ/A?
I do not have RZ/A board.

Cheers,
Biju