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

["Niklas Söderlund" <niklas.soderlund+renesas@ragnatech.se>]

Hi Wolfram and Ulf,

Thanks for working on this!

On 2020-05-15 11:26:06 +0200, Ulf Hansson wrote:
> + 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.

I had a go at this once but gave up as I only have knowledge about one 
implementation and !CONFIG_PM made it messy for me. I will see if I can 
digout the patches and see if I can recall exactly what it was. I'm sure 
it was my lack of understanding and not something technical.

> 
> 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
> >

-- 
Regards,
Niklas Söderlund