linux-kernel - Re: [PATCH 09/15] rpmsg: smd: Drop unnecessary condition for channel creation

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Date:   Mon, 31 Jan 2022 16:32:42 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     Luca Weiss <luca@...tu.xyz>, linux-arm-msm@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Andy Gross <agross@...nel.org>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: Re: [PATCH 09/15] rpmsg: smd: Drop unnecessary condition for channel
 creation

On Sun 16 Jan 10:30 CST 2022, Stephan Gerhold wrote:

> On Sun, Jan 16, 2022 at 05:08:29PM +0100, Luca Weiss wrote:
> > On Mittwoch, 12. Jänner 2022 22:39:53 CET Stephan Gerhold wrote:
> > > On Wed, Jan 12, 2022 at 08:40:58PM +0100, Luca Weiss wrote:
> > > > From: Vladimir Lypak <vladimir.lypak@...il.com>
> > > > 
> > > > RPM Firmware on variety of newer SoCs such as MSM8917 (also likely
> > > > MSM8937, MSM8940, MSM8952), MSM8953 and on some MSM8916 devices) doesn't
> > > > initiate opening of the SMD channel if it was previously opened by
> > > > bootloader. This doesn't allow probing of smd-rpm driver on such devices
> > > > because there is a check that requires RPM this behaviour.
> > > > 
> > > > Signed-off-by: Vladimir Lypak <vladimir.lypak@...il.com>
> > > > Signed-off-by: Luca Weiss <luca@...tu.xyz>
> > > > Reviewed-by: Konrad Dybcio <konrad.dybcio@...ainline.org>
> > > 
> > > This is effectively a "Revert "Revert "rpmsg: smd: Create device for all
> > > channels""":
> > > 
> > > https://lore.kernel.org/linux-arm-msm/20171212235857.10432-3-bjorn.andersson
> > > @linaro.org/
> > > https://lore.kernel.org/linux-arm-msm/20180315181244.8859-1-bjorn.andersson
> > > @linaro.org/
> > > 
> > > Won't this cause the same regression reported by Srinivas again?
> > > 
> > 
> > Do you have any suggestion on another way to solve this? Without this commit 
> > the regulators just won't probe at all, I haven't looked very deep into it 
> > though given this patch solves it.
> > 
> > I guess worst case it'll become a devicetree property to enable this quirk?
> > 
> 
> My spontaneous suggestion would be to skip the check only for the
> "rpm_requests" channel, e.g. something like
> 
> 	if (remote_state != SMD_CHANNEL_OPENING &&
> 	    remote_state != SMD_CHANNEL_OPENED &&
> 	    strcmp(channel->name, "rpm_requests")
> 		continue;
> 
> This will avoid changing the behavior for anything but the RPM channel.
> I don't think anything else is affected by the same problem (since the
> bootloader or earlier firmware should not make use of any other channel).
> Also, we definitely *always* want to open the channel to the RPM because
> otherwise almost everything breaks.
> 

Last time this came up I asked if someone could test if the RPM is stuck
in the state machine trying to close the channel and as such we could
kick it by making sure that we "ack" the closing of the channel and
hence it would come back up again.

But I don't remember seeing any outcome of this.

> Many solutions are possible though so at the end it is mostly up to
> Bjorn to decide I think. :)
> 

I would prefer to get an answer to above question, but if that doesn't
work (or look like crap) I'm willing to take your suggestion of skipping
the continue for the rpm_requests channel. Obviously with a comment
above describing why we're carrying that special case.

Regards,
Bjorn