Re: [PATCH v5 08/24] wfx: add bus_sdio.c

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

On Tue, 23 Mar 2021 at 18:53, Jérôme Pouiller
<jerome.pouiller@silabs.com> wrote:
>
> On Tuesday 23 March 2021 15:11:56 CET Ulf Hansson wrote:
> > On Mon, 22 Mar 2021 at 18:14, Jérôme Pouiller <jerome.pouiller@silabs.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@silabs.com> wrote:
> > > > >
> > > > > From: Jérôme Pouiller <jerome.pouiller@silabs.com>
> > > > >
> > > > > Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.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);

This will tell the mmc/sdio core to keep the SDIO card powered on
during system suspend. Thus, it doesn't need to re-initialize it at
system resume - and the firmware should not need to be re-programmed.

On the other hand, if you don't plan to support system wakeups, it
would probably be better to power off the card, to avoid wasting
energy while the system is suspended. I assume that means you need to
re-program the firmware as well. Normally, it's these kinds of things
that need to be managed from a ->resume() callback.

>   }
>
> 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);

I don't know what wfx_sdio_remove() does, but for sure you would need
a ->resume() callback to make it possible to restore power/firmware.

>           return 0;
>   }
>
> In both cases, I worry to provide these functions without being able to
> test them.

Alright, let's simply leave this driver without having the PM
callbacks assigned. I guess we can revisit this at some later point.

The mmc core will log a message about the missing callbacks, in case
someone tries to execute system suspend/resume when the driver has
been probed.

Kind regards
Uffe