linux-kernel - Re: [PATCH] drivers: dma: qcom: bam_dma: Manage clocks when controlled

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Date:   Sat, 23 Jan 2021 15:19:25 +0800
From:   Shawn Guo <shawn.guo@...aro.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org,
        dan.j.williams@...el.com, vkoul@...nel.org,
        srinivas.kandagatla@...aro.org, linux-arm-msm@...r.kernel.org,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: dma: qcom: bam_dma: Manage clocks when
 controlled_remotely is set

On Fri, Jan 22, 2021 at 10:44:09AM -0500, Thara Gopinath wrote:
> Hi Shawn,
> 
> Thanks for the review
> 
> On 1/22/21 12:10 AM, Shawn Guo wrote:
> > On Thu, Jan 21, 2021 at 09:52:51PM -0500, Thara Gopinath wrote:
> > > When bam dma is "controlled remotely", thus far clocks were not controlled
> > > from the Linux. In this scenario, Linux was disabling runtime pm in bam dma
> > > driver and not doing any clock management in suspend/resume hooks.
> > > 
> > > With introduction of crypto engine bam dma, the clock is a rpmh resource
> > > that can be controlled from both Linux and TZ/remote side.  Now bam dma
> > > clock is getting enabled during probe even though the bam dma can be
> > > "controlled remotely". But due to clocks not being handled properly,
> > > bam_suspend generates a unbalanced clk_unprepare warning during system
> > > suspend.
> > > 
> > > To fix the above issue and to enable proper clock-management, this patch
> > > enables runtim-pm and handles bam dma clocks in suspend/resume hooks if
> > > the clock node is present irrespective of controlled_remotely property.
> > 
> > Shouldn't the following probe code need some update?  Now we have both
> > controlled_remotely and clocks handle for cryptobam node.  For example,
> > if devm_clk_get() returns -EPROBE_DEFER, we do not want to continue with
> > bamclk forcing to be NULL, right?
> 
> We still will have to set bdev->bamclk to NULL in certain scenarios. For eg
> slimbus bam dma is controlled-remotely and the clocks are handled by the
> remote s/w. Linux does not handle the clocks at all and  there is no clock
> specified in the dt node.This is the norm for the devices that are also
> controlled by remote s/w. Crypto bam dma is a special case where the clock
> is actually a rpmh resource and hence can be independently handled from both
> remote side and Linux by voting. In this case, the dma is controlled
> remotely but clock can be turned off and on in Linux. Hence the need for
> this patch.

So is it correct to say that clock is mandatory for !controlled-remotely
BAM, while it's optional for controlled-remotely one.  If yes, maybe we
can do something like below to make the code a bit easier to read?

	if (controlled-remotely)
		bdev->bamclk = devm_clk_get_optional();
	else
		bdev->bamclk = devm_clk_get();
		
> Yes, the probe code needs updating to handle -EPROBE_DEFER (esp if the clock
> driver is built in as a module) I am not sure if the clock framework handles
> -EPROBE_DEFER properly either. So that
> might need updating too. This is a separate activity and not part of this
> patch.

As the patch breaks the assumption that for controlled-remotely BAM
there is no clock to be managed, the probe code becomes buggy right
away.

Shawn