Re: [PATCH] brcmfmac: add support for external 32khz clock

[Simon Shields <simon-WP75azK+jQYgsBAKwltoeQ@public.gmane.org>]

Hi Arend,

On Wed, Nov 08, 2017 at 11:38:11AM +0100, Arend van Spriel wrote:
> + Stefan
> 
> On 11/7/2017 2:31 PM, Simon Shields wrote:
> > Hi Arend,
> > 
> > On Tue, Nov 07, 2017 at 12:09:23PM +0100, Arend van Spriel wrote:
> > > On 11/6/2017 12:27 PM, Simon Shields wrote:
> > > > On Mon, Nov 06, 2017 at 11:59:37AM +0100, Arend van Spriel wrote:
> > > > > On 11/4/2017 2:24 PM, Simon Shields wrote:
> > > > > > Some boards use an external 32khz clock for low-power
> > > > > > mode timing. Make sure the clock is powered on while the chipset
> > > > > > is active.
> > > > > 
> > > > > Do you have such a board? With the little documentation I can get my hands
> > > > > on here I wonder whether the clock needs to be enabled before the device is
> > > > > powered. If you have the hardware I would like to check some registers in
> > > > > the device.
> > > > > 
> > > > 
> > > > Yes. Trats2 (exynos4412-based) has such a setup. The BCM4334 works fine
> > > > with this patch and one more that enables the WL_REG_EN pin when
> > > > brcmfmac is probed.
> > > 
> > > Ok. So this is exactly the thing I was wondering about. So it makes me
> > > curious how the WL_REG_EN patch looks like. Can you provide that?
> > > 
> > 
> > Here[0] is a link to the patch in its current state. Obviously, it's not
> > ready at all for mainlining :-)
> > 
> > [0]: https://github.com/fourkbomb/linux/commit/436e59e58b44d856c186fc4767560cecbcbc0c59.patch
> 
> Thanks. Indeed doing it in module_init of brcmfmac is not going to fly.
> Actually the MMC stack has a mechanism to power the SDIO device. This can be
> configured through the device tree [1]. I just checked and it actually
> includes specifying the external clock as well.
> 

It looks like mmc-pwrseq-simple would handle the clock case, but it
doesn't handle the regulator properly: it sets the GPIO to high before
powering on, then lowers it immediately after powering it on.

I guess a simpler approach here would be to extend pwrseq-simple to behave
as we need it to.

> Regards,
> Arend
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt

Cheers,
Simon