Re: [PATCH] mmc: renesas_sdhi: don't lose RPM savings because of manual clk handling

[Ulf Hansson <ulf.hansson@linaro.org>]

+ Niklas, Geert, Yamada-san,


On Wed, 13 May 2020 at 19:31, Wolfram Sang
<wsa+renesas@sang-engineering.com> wrote:
>
> The SDHI driver en-/disabled clocks on its own during probe() and
> remove(). This basically killed all potential RPM power savings. Now, we
> just enable the clocks for a short time when we access registers in
> probe(). We otherwise leave all handling to RPM. That means, we need to
> shift the RPM enabling code in the TMIO core a bit up, so we can access
> registers there, too.

No, this doesn't sound entirely right to me.

However, I do admit that we may need to move the pm_runtime
initialization earlier (perhaps even out of tmio_mmc_core), but for
slightly different reasons. Let me elaborate.

For uniphier-sd, renesas_sdhi_sys_dmac and renesas_sdhi_internal_dmac
- they all have assigned the ->clk_enable|disable() ops. Which means
they have internal clock management (calling clk_prepare|enable()
etc). For tmio_mmc, that's not the case.

On top of this, the device may also have a potential PM domain
attached. If that is the case, the PM domain may or may not have clock
management implemented through genpd's ->start|stop() callbacks.

So, in the end we are going to have to rely on clock enable/prepare
reference counting, as we have to manage the clock(s) at both the
driver and the PM domain level. Taking into account all various
combinations (and that CONFIG_PM may not always be set). I have
started to hack on some patches, but before I share them, let me ask a
few questions.

1. tmio_mmc: - is that used solely with clock management through
genpd? Or has no clock management at all?
2. uniphier-sd: Don't have runtime PM callbacks assigned. It looks
like it doesn't care about runtime PM, but maybe it does through a PM
domain? Can we skip to enable runtime PM for uniphier-sd, no?

Kind regards
Uffe

>
> clk_summary before:
> sd0                   1        1        0    12480000          0     0  50000
>    sdif0              2        2        0    12480000          0     0  50000
>
> clk_summary after:
> sd0                   1        1        0    12480000          0     0  50000
>    sdif0              1        1        0    12480000          0     0  50000
>
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
>
> Tested on a Salvator-XS board with R-Car M3-N.
>
>  drivers/mmc/host/renesas_sdhi_core.c |  7 +++----
>  drivers/mmc/host/tmio_mmc_core.c     | 14 +++++++-------
>  2 files changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/mmc/host/renesas_sdhi_core.c b/drivers/mmc/host/renesas_sdhi_core.c
> index ff72b381a6b3..d581142634f8 100644
> --- a/drivers/mmc/host/renesas_sdhi_core.c
> +++ b/drivers/mmc/host/renesas_sdhi_core.c
> @@ -910,6 +910,8 @@ int renesas_sdhi_probe(struct platform_device *pdev,
>                 goto efree;
>
>         ver = sd_ctrl_read16(host, CTL_VERSION);
> +       renesas_sdhi_clk_disable(host);
> +
>         /* GEN2_SDR104 is first known SDHI to use 32bit block count */
>         if (ver < SDHI_VER_GEN2_SDR104 && mmc_data->max_blk_count > U16_MAX)
>                 mmc_data->max_blk_count = U16_MAX;
> @@ -920,7 +922,7 @@ int renesas_sdhi_probe(struct platform_device *pdev,
>
>         ret = tmio_mmc_host_probe(host);
>         if (ret < 0)
> -               goto edisclk;
> +               goto efree;
>
>         /* Enable tuning iff we have an SCC and a supported mode */
>         if (of_data && of_data->scc_offset &&
> @@ -985,8 +987,6 @@ int renesas_sdhi_probe(struct platform_device *pdev,
>
>  eirq:
>         tmio_mmc_host_remove(host);
> -edisclk:
> -       renesas_sdhi_clk_disable(host);
>  efree:
>         tmio_mmc_host_free(host);
>
> @@ -999,7 +999,6 @@ int renesas_sdhi_remove(struct platform_device *pdev)
>         struct tmio_mmc_host *host = platform_get_drvdata(pdev);
>
>         tmio_mmc_host_remove(host);
> -       renesas_sdhi_clk_disable(host);
>
>         return 0;
>  }
> diff --git a/drivers/mmc/host/tmio_mmc_core.c b/drivers/mmc/host/tmio_mmc_core.c
> index 9a4ae954553b..6968177dd1cd 100644
> --- a/drivers/mmc/host/tmio_mmc_core.c
> +++ b/drivers/mmc/host/tmio_mmc_core.c
> @@ -1116,6 +1116,13 @@ int tmio_mmc_host_probe(struct tmio_mmc_host *_host)
>
>         _host->set_pwr = pdata->set_pwr;
>
> +       dev_pm_domain_start(&pdev->dev);
> +       pm_runtime_get_noresume(&pdev->dev);
> +       pm_runtime_set_active(&pdev->dev);
> +       pm_runtime_set_autosuspend_delay(&pdev->dev, 50);
> +       pm_runtime_use_autosuspend(&pdev->dev);
> +       pm_runtime_enable(&pdev->dev);
> +
>         ret = tmio_mmc_init_ocr(_host);
>         if (ret < 0)
>                 return ret;
> @@ -1192,13 +1199,6 @@ int tmio_mmc_host_probe(struct tmio_mmc_host *_host)
>         /* See if we also get DMA */
>         tmio_mmc_request_dma(_host, pdata);
>
> -       dev_pm_domain_start(&pdev->dev);
> -       pm_runtime_get_noresume(&pdev->dev);
> -       pm_runtime_set_active(&pdev->dev);
> -       pm_runtime_set_autosuspend_delay(&pdev->dev, 50);
> -       pm_runtime_use_autosuspend(&pdev->dev);
> -       pm_runtime_enable(&pdev->dev);
> -
>         ret = mmc_add_host(mmc);
>         if (ret)
>                 goto remove_host;
> --
> 2.20.1
>