linux-kernel - Re: [RESEND PATCH] amba: Allow pclk to be controlled by power domain

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Message-ID: <CAPDyKFrWZ5C=rp7_ad0Pvz-GFb20yU+BZn_hEHxR_6DDBW8zrQ@mail.gmail.com>
Date:   Thu, 21 Feb 2019 08:55:00 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Subject: Re: [RESEND PATCH] amba: Allow pclk to be controlled by power domain

On Tue, 19 Feb 2019 at 07:43, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Tue 05 Feb 06:58 PST 2019, Ulf Hansson wrote:
>
> > On Thu, 31 Jan 2019 at 03:01, Bjorn Andersson
> > <bjorn.andersson@...aro.org> wrote:
> > >
> > > On the Qualcomm SDM845 platform the apb_pclk is controlled as part of
> > > the QDSS power/clock domain. Handle this by allowing amba to operate
> > > without direct apb_pclk control, when a powerdomain is attached and no
> > > clock is described.
> > >
> > > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > > ---
> > >
> > > Resending this separate from the series it was originally part of.
> > >
> > >  drivers/amba/bus.c | 9 +++++++--
> > >  1 file changed, 7 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> > > index 41b706403ef7..3e13050c6d59 100644
> > > --- a/drivers/amba/bus.c
> > > +++ b/drivers/amba/bus.c
> > > @@ -219,8 +219,13 @@ static int amba_get_enable_pclk(struct amba_device *pcdev)
> > >         int ret;
> > >
> > >         pcdev->pclk = clk_get(&pcdev->dev, "apb_pclk");
> > > -       if (IS_ERR(pcdev->pclk))
> > > -               return PTR_ERR(pcdev->pclk);
> > > +       if (IS_ERR(pcdev->pclk)) {
> > > +               /* Continue with no clock specified, but pm_domain attached */
> > > +               if (PTR_ERR(pcdev->pclk) == -ENOENT && pcdev->dev.pm_domain)
> > > +                       pcdev->pclk = NULL;
> >
> > This looks fragile to me.
> >
> > I would prefer to make a do match with DT, to check whether the clock
> > is needed or not.
>
> Can you please elaborate on what you want me to match on?
>
> As an example you can find the patch depending on this here:
> https://lore.kernel.org/lkml/60ebf1617f0285c89e921bf3839cba6906d493c9.1548419933.git.saiprakash.ranjan@codeaurora.org/

I would extend the compatible with a "soc-id" prefix and match on that.

If that doesn't work, I guess we need check for the soc family/id,
thus use soc_device_match().

>
> > Moreover, there should be no reason to check for the
> > ->dev.pm_domain, because, if there was an error while doing the
> > attach, that should already have been reported/propagated.
> >
>
> The purpose of this check was to extend the current requirement of a
> clock to require either a clock or a power domain, rather than just
> making the clock optional - which would be the result if this part is
> omitted.

Well, that would break the current requirement for everybody else,
which is that the clock is required and the PM domain is optional.

[...]

Kind regards
Uffe