netdev - Re: [PATCH v5 08/24] wfx: add bus

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Date:   Tue, 23 Mar 2021 18:53:46 +0100
From:   Jérôme Pouiller <jerome.pouiller@...abs.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        driverdevel <devel@...verdev.osuosl.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        DTML <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Pali Rohár <pali@...nel.org>
Subject: Re: [PATCH v5 08/24] wfx: add bus_sdio.c

On Tuesday 23 March 2021 15:11:56 CET Ulf Hansson wrote:
> On Mon, 22 Mar 2021 at 18:14, Jérôme Pouiller <jerome.pouiller@...abs.com> wrote:
> > On Monday 22 March 2021 13:20:35 CET Ulf Hansson wrote:
> > > On Mon, 15 Mar 2021 at 14:25, Jerome Pouiller <Jerome.Pouiller@...abs.com> wrote:
> > > >
> > > > From: Jérôme Pouiller <jerome.pouiller@...abs.com>
> > > >
> > > > Signed-off-by: Jérôme Pouiller <jerome.pouiller@...abs.com>
> > > > ---
> > > >  drivers/net/wireless/silabs/wfx/bus_sdio.c | 259 +++++++++++++++++++++
> > > >  1 file changed, 259 insertions(+)
> > > >  create mode 100644 drivers/net/wireless/silabs/wfx/bus_sdio.c
> > >
> > > [...]
> > >
> > > > +static const struct sdio_device_id wfx_sdio_ids[] = {
> > > > +       { SDIO_DEVICE(SDIO_VENDOR_ID_SILABS, SDIO_DEVICE_ID_SILABS_WF200) },
> > > > +       { },
> > > > +};
> > > > +MODULE_DEVICE_TABLE(sdio, wfx_sdio_ids);
> > > > +
> > > > +struct sdio_driver wfx_sdio_driver = {
> > > > +       .name = "wfx-sdio",
> > > > +       .id_table = wfx_sdio_ids,
> > > > +       .probe = wfx_sdio_probe,
> > > > +       .remove = wfx_sdio_remove,
> > > > +       .drv = {
> > > > +               .owner = THIS_MODULE,
> > > > +               .of_match_table = wfx_sdio_of_match,
> > >
> > > It's not mandatory to support power management, like system
> > > suspend/resume. However, as this looks like this is a driver for an
> > > embedded SDIO device, you probably want this.
> > >
> > > If that is the case, please assign the dev_pm_ops here and implement
> > > the ->suspend|resume() callbacks.
> >
> > I have no platform to test suspend/resume, so I have only a
> > theoretical understanding of this subject.
> 
> I see.
> 
> >
> > I understanding is that with the current implementation, the
> > device will be powered off on suspend and then totally reset
> > (including reloading of the firmware) on resume. I am wrong?
> 
> You are correct, for a *removable* SDIO card. In this case, the
> mmc/sdio core will remove the corresponding SDIO card/device and its
> corresponding SDIO func devices at system suspend. It will then be
> redetected at system resume (and the SDIO func driver re-probed).
> 
> Although, as this is an embedded SDIO device, per definition it's not
> a removable card (MMC_CAP_NONREMOVABLE should be set for the
> corresponding mmc host), the SDIO card will stick around and instead
> the ->suspend|resume() callback needs to be implemented for the SDIO
> func driver.

If I follow what has been done in other drivers I would write something
like:

  static int wfx_sdio_suspend(struct device *dev)
  {
          struct sdio_func *func = dev_to_sdio_func(dev);
          struct wfx_sdio_priv *bus = sdio_get_drvdata(func);

          config_reg_write_bits(bus->core, CFG_IRQ_ENABLE_DATA, 0);
          // Necessary to keep device firmware in RAM
          return sdio_set_host_pm_flags(func, MMC_PM_KEEP_POWER);
  }

However, why not the implementation below?

  static int wfx_sdio_suspend(struct device *dev)
  {
          struct sdio_func *func = dev_to_sdio_func(dev);

          wfx_sdio_remove(func);
          return 0;
  }

In both cases, I worry to provide these functions without being able to
test them.


-- 
Jérôme Pouiller