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

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Date:   Mon, 18 Feb 2019 22:43:42 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Ulf Hansson <ulf.hansson@...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 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/

> 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.

Regards,
Bjorn

> > +               else
> > +                       return PTR_ERR(pcdev->pclk);
> > +       }
> >
> >         ret = clk_prepare_enable(pcdev->pclk);
> >         if (ret)
> > --
> > 2.18.0
> >
> 
> Kind regards
> Uffe