linux-kernel - Re: [PATCH v4 02/10] dmaengine: Actions: Add support for S700 DMA engine

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Date:   Mon, 29 Jun 2020 13:58:31 +0530
From:   Amit Tomer <amittomer25@...il.com>
To:     André Przywara <andre.przywara@....com>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        dan.j.williams@...el.com, cristian.ciocaltea@...il.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-actions@...ts.infradead.org
Subject: Re: [PATCH v4 02/10] dmaengine: Actions: Add support for S700 DMA engine

Hi,

On Wed, Jun 24, 2020 at 3:06 PM André Przywara <andre.przywara@....com> wrote:
>
> On 24/06/2020 07:15, Vinod Koul wrote:
>
> Hi,
>
> > On 09-06-20, 15:47, Amit Singh Tomar wrote:
> >
> >> @@ -372,6 +383,7 @@ static inline int owl_dma_cfg_lli(struct owl_dma_vchan *vchan,
> >>                                struct dma_slave_config *sconfig,
> >>                                bool is_cyclic)
> >>  {
> >> +    struct owl_dma *od = to_owl_dma(vchan->vc.chan.device);
> >>      u32 mode, ctrlb;
> >>
> >>      mode = OWL_DMA_MODE_PW(0);
> >> @@ -427,14 +439,26 @@ static inline int owl_dma_cfg_lli(struct owl_dma_vchan *vchan,
> >>      lli->hw[OWL_DMADESC_DADDR] = dst;
> >>      lli->hw[OWL_DMADESC_SRC_STRIDE] = 0;
> >>      lli->hw[OWL_DMADESC_DST_STRIDE] = 0;
> >> -    /*
> >> -     * Word starts from offset 0xC is shared between frame length
> >> -     * (max frame length is 1MB) and frame count, where first 20
> >> -     * bits are for frame length and rest of 12 bits are for frame
> >> -     * count.
> >> -     */
> >> -    lli->hw[OWL_DMADESC_FLEN] = len | FCNT_VAL << 20;
> >> -    lli->hw[OWL_DMADESC_CTRLB] = ctrlb;
> >> +
> >> +    if (od->devid == S700_DMA) {
> >> +            /* Max frame length is 1MB */
> >> +            lli->hw[OWL_DMADESC_FLEN] = len;
> >> +            /*
> >> +             * On S700, word starts from offset 0x1C is shared between
> >> +             * frame count and ctrlb, where first 12 bits are for frame
> >> +             * count and rest of 20 bits are for ctrlb.
> >> +             */
> >> +            lli->hw[OWL_DMADESC_CTRLB] = FCNT_VAL | ctrlb;
> >> +    } else {
> >> +            /*
> >> +             * On S900, word starts from offset 0xC is shared between
> >> +             * frame length (max frame length is 1MB) and frame count,
> >> +             * where first 20 bits are for frame length and rest of
> >> +             * 12 bits are for frame count.
> >> +             */
> >> +            lli->hw[OWL_DMADESC_FLEN] = len | FCNT_VAL << 20;
> >> +            lli->hw[OWL_DMADESC_CTRLB] = ctrlb;
> >
> > Unfortunately this wont scale, we will keep adding new conditions for
> > newer SoC's! So rather than this why not encode max frame length in
> > driver_data rather than S900_DMA/S700_DMA.. In future one can add values
> > for newer SoC and not code above logic again.
>
> What newer SoCs? I don't think we should try to guess the future here.
> We can always introduce further abstractions later, once we actually
> *know* what we are looking at.
>
Apart from it , we have *one* more SoC from Actions .i.e. S500 where
the DMA controller is
identical to S900, and requires *no* additional code to work properly.

So, I think we are safe to have the changes proposed in this patch.

Thanks

-Amit