From: Marc Zyngier <maz@kernel.org>
To: Shawn Guo <shawn.guo@linaro.org>
Cc: Maulik Shah <quic_mkshah@quicinc.com>,
Thomas Gleixner <tglx@linutronix.de>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
Loic Poulain <loic.poulain@linaro.org>,
devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/2] irqchip: Add Qualcomm MPM controller driver
Date: Tue, 30 Nov 2021 08:52:45 +0000 [thread overview]
Message-ID: <87ilwam3du.wl-maz@kernel.org> (raw)
In-Reply-To: <20211130083143.GF10105@dragon>
On Tue, 30 Nov 2021 08:31:44 +0000,
Shawn Guo <shawn.guo@linaro.org> wrote:
>
> On Tue, Nov 30, 2021 at 01:19:48PM +0530, Maulik Shah wrote:
> > Hi Shawn,
> >
> > On 11/30/2021 8:01 AM, Shawn Guo wrote:
> >
> > + do {
> > + r_val = readl(priv->base + offset);
> > + udelay(5);
> > + } while (r_val != val);
> >
> > What? Is this waiting for a bit to clear? Why isn't this one of the
> > read*_poll_timeout*() function instead? Surely you can't wait forever
> > here.
> >
> > This is taken from downstream, and it seems to double check the written
> > value by reading it back. But to be honest, I'm not really this is
> > necessary. I will do some testing with the read-back check dropped.
> >
> > How about asking for specs instead? There are QC people on Cc, and
> > many more reading the list. Hopefully they can explain what this is
> > all about.
> >
> > Maulik,
> >
> > If you have some information about this, that would be great.
> >
> > This can be converted to read poll_timeout(). This was introduced in
> > place of wmb() to make sure writes are completed.
>
> Hmm, in this case, writel() will just do the right thing, as it wraps
> wmb() there. Or am I missing something?
writel() places the wmb() *before* the MMIO access. This is use for
ordering with RAM access if the device is DMA capable, for example. I
seriously doubt this is the case.
My understanding of Maulik's comment is that there is a requirement
for the MMIO access to complete. And for that, a barrier *after* the
write is the right tool for the job.
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2021-11-30 8:52 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-26 9:35 [PATCH v2 0/2] Add Qualcomm MPM irqchip driver support Shawn Guo
2021-11-26 9:35 ` [PATCH v2 1/2] dt-bindings: interrupt-controller: Add Qualcomm MPM support Shawn Guo
2021-12-01 23:02 ` Rob Herring
2021-11-26 9:35 ` [PATCH v2 2/2] irqchip: Add Qualcomm MPM controller driver Shawn Guo
2021-11-26 15:13 ` Marc Zyngier
2021-11-26 19:19 ` Marc Zyngier
2021-11-29 13:33 ` Shawn Guo
2021-11-29 15:24 ` Marc Zyngier
2021-11-30 2:31 ` Shawn Guo
2021-11-30 8:42 ` Marc Zyngier
2021-11-30 9:17 ` Shawn Guo
2021-11-30 10:44 ` Marc Zyngier
2021-12-01 7:36 ` Shawn Guo
[not found] ` <2e821841-a921-3fda-9ee6-3d5127653033@quicinc.com>
2021-11-30 8:31 ` Shawn Guo
2021-11-30 8:52 ` Marc Zyngier [this message]
2021-11-30 8:54 ` Maulik Shah
2021-11-30 8:47 ` Marc Zyngier
2021-11-27 7:49 ` kernel test robot
2021-11-29 7:23 ` Maulik Shah
2021-11-29 13:45 ` Shawn Guo
2021-11-30 8:26 ` Maulik Shah
2021-11-30 8:44 ` Shawn Guo
2021-11-30 9:04 ` Maulik Shah
2021-11-30 9:26 ` Shawn Guo
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