linux-kernel - Re: [PATCH] soc: imx: gpcv2: keep i.MX8MM VPU-H1 bus clock active

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Date:   Tue, 5 Apr 2022 14:44:58 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Adam Ford <aford173@...il.com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Tim Harvey <tharvey@...eworks.com>,
        Adam Ford-BE <aford@...conembedded.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Peng Fan <peng.fan@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] soc: imx: gpcv2: keep i.MX8MM VPU-H1 bus clock active

On Thu, Mar 31, 2022 at 06:32:13AM -0500, Adam Ford wrote:
> On Thu, Mar 31, 2022 at 4:28 AM Lucas Stach <l.stach@...gutronix.de> wrote:
> >
> > Hi Adam, hi Shawn,
> >
> > Am Samstag, dem 20.11.2021 um 13:39 -0600 schrieb Adam Ford:
> > > Enable the vpu-h1 clock when the domain is active because reading
> > > or writing to the VPU-H1 IP block cause the system to hang.
> > >
> > > Fixes: 656ade7aa42a ("soc: imx: gpcv2: keep i.MX8M* bus clocks enabled")
> > > Signed-off-by: Adam Ford <aford173@...il.com>
> > >
> > > diff --git a/drivers/soc/imx/gpcv2.c b/drivers/soc/imx/gpcv2.c
> > > index b8d52d8d29db..7b6dfa33dcb9 100644
> > > --- a/drivers/soc/imx/gpcv2.c
> > > +++ b/drivers/soc/imx/gpcv2.c
> > > @@ -734,6 +734,7 @@ static const struct imx_pgc_domain imx8mm_pgc_domains[] = {
> > >                       .map = IMX8MM_VPUH1_A53_DOMAIN,
> > >               },
> > >               .pgc   = BIT(IMX8MM_PGC_VPUH1),
> > > +             .keep_clocks = true,
> > >       },
> > >
> > I missed this patch and just stumbled across it when looking at the git
> > history. I don't think this patch is correct. The H1 GPC domain does
> > not even have clocks assigned in the DT, so there is nothing to keep
> > active. Also H1 is not a MIX domain, so it should not keep any bus
> > clocks active, that is the job of the VPUMIX domain.
> >
> > While this patch is a no-op, as far as I can see, it still seems wrong
> > and I think it should be reverted.
> 
> At the time I sent this, I was working with some people in the media
> group to split the G1 and G2 up in the imx8mq and add G1 and G2
> support in the imx8mm.  I had inquired about the feasibility of using
> the H1 encoder on the imx8mm, but I needed to read some registers from
> the IP block to see which features were fused out.  I tried several
> different options to get the H1 to not hang when reading registers,
> and that was the only solution I found that worked.  I thought it odd
> as well since the G1 and G2 decoders didn't appear to need this.
> However, during the course of my investigation, I learned that the
> JPEG encoder was fused out of the imx8mm, and there wasn't a plan to
> add VP8 or H.264 encodering any time soon.   Since it is, as you put
> it, a no-op, I have no objections to reverting it.

I do not quite follow.  You claimed that the change fixes a system hang.
Are we getting the hang back if we revert the change?

Shawn