linux-kernel - Re: [PATCH] dmaengine: qcom: bam_dma: make channels/EEs optional in DT with clock

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Message-ID: <ZGdMMd3pS7LRjBOU@gerhold.net>
Date:   Fri, 19 May 2023 12:15:13 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Bhupesh Sharma <bhupesh.sharma@...aro.org>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: make channels/EEs optional in
 DT with clock

On Fri, May 19, 2023 at 02:40:21PM +0530, Bhupesh Sharma wrote:
> On Thu, 18 May 2023 at 16:51, Stephan Gerhold <stephan@...hold.net> wrote:
> >
> > On Thu, May 18, 2023 at 04:43:57PM +0530, Bhupesh Sharma wrote:
> > > On Thu, 18 May 2023 at 14:56, Stephan Gerhold <stephan@...hold.net> wrote:
> > > >
> > > > If we have a BAM clock in the DT we are able to turn on the BAM
> > > > controller while probing, so there is no need to read "num-channels"
> > > > and "qcom,num-ees" from the DT. It can be read more accurately directly
> > > > from the identification registers of the BAM.
> > > >
> > > > This simplifies setting up typical controlled-remotely BAM DMAs in the
> > > > DT that can be turned on via a clock (e.g. the BLSP DMA).
> > >
> > > Can you please list which qcom board(s) you tested this patch on?
> > >
> >
> > It works fine at least on MSM8916/DB410c (for blsp_dma) and MDM9607
> > (blsp_dma and qpic_dma (for NAND)). More testing would be much
> > appreciated of course!
> 
> I tested this yesterday on RB1/RB2, RB5 and saw no improvement, so was wondering
> why exactly is this needed and which platforms are impacted.
> 

RB1/RB2 should be able to benefit from this for the cryptobam if you add
the rpmcc clock to it, see my reply in [1].

[1]: https://lore.kernel.org/linux-arm-msm/ZGdLCdSof027mk5u@gerhold.net/

> > Personally I don't see much of a risk: If enabling the clock doesn't
> > actually enable the BAM controller, then the clock probably does not
> > belong to the BAM in the first place... :)
> 
> Right, but I think the commit message needs a bit more clarity to
> reflect that it is now proposed to check for the bam_clk presence
> earlier in the _probe flow (as compared to earlier).
> 

Sure, I will try to clarify the commit message a bit in v2.

Thanks,
Stephan