Re: [PATCH v3] dmaengine: sh: rz-dmac: Add device_synchronize callback

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Hi Biju,

On Thu, Jul 21, 2022 at 4:49 PM Biju Das <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> Some on-chip peripheral modules(for eg:- rspi) on RZ/G2L SoC
> use the same signal for both interrupt and DMA transfer requests.
> The signal works as a DMA transfer request signal by setting
> DMARS, and subsequent interrupt requests to the interrupt controller
> are masked.
>
> We can re-enable the interrupt by clearing the DMARS.
>
> This patch adds device_synchronize callback for clearing
> DMARS and thereby allowing DMA consumers to switch to
> interrupt mode.
>
> Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> ---
> v2->v3:
>  * Fixed commit description
>  * Added check if the DMA operation has been completed or terminated,
>    and wait (sleep) if needed.

Thanks for the uodate!

> --- a/drivers/dma/sh/rz-dmac.c
> +++ b/drivers/dma/sh/rz-dmac.c
> @@ -12,6 +12,7 @@
>  #include <linux/dma-mapping.h>
>  #include <linux/dmaengine.h>
>  #include <linux/interrupt.h>
> +#include <linux/iopoll.h>
>  #include <linux/list.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -630,6 +631,21 @@ static void rz_dmac_virt_desc_free(struct virt_dma_desc *vd)
>          */
>  }
>
> +static void rz_dmac_device_synchronize(struct dma_chan *chan)
> +{
> +       struct rz_dmac_chan *channel = to_rz_dmac_chan(chan);
> +       struct rz_dmac *dmac = to_rz_dmac(chan->device);
> +       u32 chstat;
> +       int ret;
> +
> +       ret = read_poll_timeout(rz_dmac_ch_readl, chstat, !(chstat & CHSTAT_EN),
> +                               10, 1000, false, channel, CHSTAT, 1);

Isn't 1000 µs = 1 ms a bit short?
IIUIC, I can submit a DMA operation for transfering a 64 KiB (or larger)
block, and call dmaengine_synchronize() immediately after that?

> +       if (ret < 0)
> +               dev_warn(dmac->dev, "DMA Timeout");
> +
> +       rz_dmac_set_dmars_register(dmac, channel->index, 0);
> +}
> +
>  /*
>   * -----------------------------------------------------------------------------
>   * IRQ handling

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds



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