linux-kernel - Re: [PATCH] power: sequencing: qcom-wcn: explain why we need the WLAN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAMRc=Mf7bcfD3+vu9veWrd44hqiHZZnSgiiaObeMUfajLRqPmQ@mail.gmail.com>
Date: Tue, 17 Dec 2024 16:09:04 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Stephan Gerhold <stephan.gerhold@...aro.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] power: sequencing: qcom-wcn: explain why we need the
 WLAN_EN GPIO hack

On Tue, Dec 17, 2024 at 3:03 PM Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.org> wrote:
>
> On Tue, Dec 17, 2024 at 02:07:14PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > With the recent rework of the PCI power control code, the workaround for
> > the wlan-enable GPIO - where we don't set a default (low) state in the
> > power sequencing driver, but instead request the pin as-is - should no
> > longer be needed but some platforms still fail to probe the WLAN
> > controller. This is caused by the Qcom PCIe controller and needs a
> > workaround in the controller driver so add a FIXME to eventually remove
> > the hack from this driver once this is done.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> >  drivers/power/sequencing/pwrseq-qcom-wcn.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/power/sequencing/pwrseq-qcom-wcn.c b/drivers/power/sequencing/pwrseq-qcom-wcn.c
> > index cc03b5aaa8f2..9d6a68ac719f 100644
> > --- a/drivers/power/sequencing/pwrseq-qcom-wcn.c
> > +++ b/drivers/power/sequencing/pwrseq-qcom-wcn.c
> > @@ -396,6 +396,14 @@ static int pwrseq_qcom_wcn_probe(struct platform_device *pdev)
> >               return dev_err_probe(dev, PTR_ERR(ctx->bt_gpio),
> >                                    "Failed to get the Bluetooth enable GPIO\n");
> >
> > +     /*
> > +      * FIXME: This should actually be GPIOD_OUT_LOW. The driver model can
> > +      * correctly handle provider <-> consumer dependencies but there is a
> > +      * known issue with Qcom PCIe controllers where, if the device is
> > +      * powered off abrubtly (without controller driver noticing), the PCIe
> > +      * link moves to link down state. Until the link-down handling is
> > +      * addressed in the controller driver, we need to keep this workaround.
>
> Maybe we should add some info on how GPIOD_OUT_LOW causes link down. Like,
>

Sure.

>         /*
>          * FIXME: This should actually be GPIOD_OUT_LOW. But doing so would
>          * cause the WLAN power to be toggled, resulting in PCIe link down.
>          * Since the PCIe controller driver is not handling link down currently,
>          * the device becomes unusable. So we need to keep this workaround until
>          * the link down handling is implemented in the controller driver.
>          */
>
> But the comment applies to gpiod_direction_output() call as well, right?
>

Yes, but there is already a comment above it.

Bartosz