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

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Date:   Fri, 19 May 2023 14:40:21 +0530
From:   Bhupesh Sharma <bhupesh.sharma@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
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 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.

> 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).

Thanks.