Message-ID: <CAMuHMdU8WQsA_tXTpDvv0HQ1j=mawyJ2sMk3nuJJXgJxHOTeoA@mail.gmail.com>
Date: Wed, 3 Sep 2025 14:17:53 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Tommaso Merciai <tommaso.merciai.xr@...renesas.com>
Cc: tomm.merciai@...il.com, linux-renesas-soc@...r.kernel.org, 
	biju.das.jz@...renesas.com, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Vinod Koul <vkoul@...nel.org>, 
	Philipp Zabel <p.zabel@...gutronix.de>, Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Uwe Kleine-König <u.kleine-koenig@...libre.com>, 
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, 
	dmaengine@...r.kernel.org
Subject: Re: [PATCH v2 5/5] dmaengine: sh: rz-dmac: Add runtime PM support

Hi Tommaso,

Thanks for your patch!

I don't understand why you included this patch in a series with clock
patches. AFAIUC, there is no dependency.  Am I missing something?

On Wed, 3 Sept 2025 at 10:28, Tommaso Merciai
<tommaso.merciai.xr@...renesas.com> wrote:
> Enable runtime power management in the rz-dmac driver by adding suspend and
> resume callbacks. This ensures the driver can correctly assert and deassert

This is not really what this patch does: the Runtime PM-related changes
just hide^Wmove reset handling into the runtime callbacks.

> the reset control and manage power state transitions during suspend and
> resume. Adding runtime PM support allows the DMA controller to reduce power

(I assume) This patch does fix resuming from _system_ suspend.

> consumption when idle and maintain correct operation across system sleep
> states, addressing the previous lack of dynamic power management in the
> driver.

The driver still does not do dynamic power management: you still call
pm_runtime_resume_and_get() from the driver's probe() .callback, and
call pm_runtime_put() only from the .remove() callback, so the device
is powered all the time.
To implement dynamic power management, you have to change that,
and call pm_runtime_resume_and_get() and pm_runtime_put() from the
.device_alloc_chan_resources() resp. .device_free_chan_resources()
callbacks (see e.g. drivers/dma/sh/rcar-dmac.c).

> Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@...renesas.com>

> --- a/drivers/dma/sh/rz-dmac.c
> +++ b/drivers/dma/sh/rz-dmac.c
> @@ -437,6 +437,17 @@ static int rz_dmac_xfer_desc(struct rz_dmac_chan *chan)
>   * DMA engine operations
>   */
>
> +static void rz_dmac_chan_init_all(struct rz_dmac *dmac)
> +{
> +       unsigned int i;
> +
> +       rz_dmac_writel(dmac, DCTRL_DEFAULT, CHANNEL_0_7_COMMON_BASE + DCTRL);
> +       rz_dmac_writel(dmac, DCTRL_DEFAULT, CHANNEL_8_15_COMMON_BASE + DCTRL);
> +
> +       for (i = 0; i < dmac->n_channels; i++)
> +               rz_dmac_ch_writel(&dmac->channels[i], CHCTRL_DEFAULT, CHCTRL, 1);
> +}
> +
>  static int rz_dmac_alloc_chan_resources(struct dma_chan *chan)
>  {
>         struct rz_dmac_chan *channel = to_rz_dmac_chan(chan);
> @@ -970,10 +981,6 @@ static int rz_dmac_probe(struct platform_device *pdev)
>                 goto err_pm_disable;
>         }
>
> -       ret = reset_control_deassert(dmac->rstc);
> -       if (ret)
> -               goto err_pm_runtime_put;
> -
>         for (i = 0; i < dmac->n_channels; i++) {
>                 ret = rz_dmac_chan_probe(dmac, &dmac->channels[i], i);
>                 if (ret < 0)
> @@ -1028,8 +1035,6 @@ static int rz_dmac_probe(struct platform_device *pdev)
>                                   channel->lmdesc.base_dma);
>         }
>
> -       reset_control_assert(dmac->rstc);
> -err_pm_runtime_put:
>         pm_runtime_put(&pdev->dev);
>  err_pm_disable:
>         pm_runtime_disable(&pdev->dev);
> @@ -1052,13 +1057,50 @@ static void rz_dmac_remove(struct platform_device *pdev)
>                                   channel->lmdesc.base,
>                                   channel->lmdesc.base_dma);
>         }
> -       reset_control_assert(dmac->rstc);
>         pm_runtime_put(&pdev->dev);
>         pm_runtime_disable(&pdev->dev);
>
>         platform_device_put(dmac->icu.pdev);
>  }
>
> +static int rz_dmac_runtime_suspend(struct device *dev)
> +{
> +       struct rz_dmac *dmac = dev_get_drvdata(dev);
> +
> +       return reset_control_assert(dmac->rstc);

Do you really want to reset the device (and thus loose register state)
each and every time the device is runtime-suspended?  For now it doesn't
matter much, but once you implement real dynamic power management,
it does.
I think the reset handling should be moved to the system suspend/resume
callbacks.

> +}
> +
> +static int rz_dmac_runtime_resume(struct device *dev)
> +{
> +       struct rz_dmac *dmac = dev_get_drvdata(dev);
> +
> +       return reset_control_deassert(dmac->rstc);

Shouldn't this reinitialize some registers?
For now that indeed doesn't matter, as reset is only deasserted
from .probe(), before any register initialization.

> +}
> +
> +static int rz_dmac_resume(struct device *dev)
> +{
> +       struct rz_dmac *dmac = dev_get_drvdata(dev);
> +       int ret;
> +
> +       ret = pm_runtime_force_resume(dev);
> +       if (ret)
> +               return ret;
> +
> +       rz_dmac_chan_init_all(dmac);
> +
> +       return 0;
> +}
> +
> +static const struct dev_pm_ops rz_dmac_pm_ops = {
> +       /*
> +        * TODO for system sleep/resume:
> +        *   - Wait for the current transfer to complete and stop the device,
> +        *   - Resume transfers, if any.
> +        */
> +       NOIRQ_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend, rz_dmac_resume)
> +       RUNTIME_PM_OPS(rz_dmac_runtime_suspend, rz_dmac_runtime_resume, NULL)
> +};
> +
>  static const struct of_device_id of_rz_dmac_match[] = {
>         { .compatible = "renesas,r9a09g057-dmac", },
>         { .compatible = "renesas,rz-dmac", },
> @@ -1068,6 +1110,7 @@ MODULE_DEVICE_TABLE(of, of_rz_dmac_match);
>
>  static struct platform_driver rz_dmac_driver = {
>         .driver         = {
> +               .pm     = pm_ptr(&rz_dmac_pm_ops),
>                 .name   = "rz-dmac",
>                 .of_match_table = of_rz_dmac_match,
>         },

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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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