linux-kernel - Re: [PATCH v4] dmaengine: qcom: bam_dma: Avoid writing unavailable register

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Message-ID: <Z35dG7J8BLzeoT3B@vaman>
Date: Wed, 8 Jan 2025 16:40:19 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Georgi Djakov <djakov@...nel.org>
Cc: Md Sadre Alam <quic_mdalam@...cinc.com>, linux-arm-msm@...r.kernel.org,
	dmaengine@...r.kernel.org, quic_mmanikan@...cinc.com,
	quic_srichara@...cinc.com, quic_varada@...cinc.com,
	robin.murphy@....com, u.kleine-koenig@...libre.com,
	martin.petersen@...cle.com, fenghua.yu@...el.com,
	av2082000@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] dmaengine: qcom: bam_dma: Avoid writing unavailable
 register

On 07-01-25, 23:30, Georgi Djakov wrote:
> On 20.12.24 11:42, Md Sadre Alam wrote:
> > Avoid writing unavailable register in BAM-Lite mode.
> > BAM_DESC_CNT_TRSHLD register is unavailable in BAM-Lite
> > mode. Its only available in BAM-NDP mode. So only write
> > this register for clients who is using BAM-NDP.
> > 
> > Signed-off-by: Md Sadre Alam <quic_mdalam@...cinc.com>
> > ---
> 
> My Dragonboard db845c fails to boot on recent linux-next releases and
> git bisect points to this patch. It boots again when it's reverted.

Should we revert?

> 
> [..]
> 
> >   	bchan->reconfigure = 0;
> > @@ -1192,10 +1199,11 @@ static int bam_init(struct bam_device *bdev)
> >   	u32 val;
> >   	/* read revision and configuration information */
> > -	if (!bdev->num_ees) {
> > -		val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
> > +	val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
> > +	if (!bdev->num_ees)
> >   		bdev->num_ees = (val >> NUM_EES_SHIFT) & NUM_EES_MASK;
> > -	}
> > +
> > +	bdev->bam_revision = val & REVISION_MASK;
> 
> The problem seems to occur when we try to read the revision for the
> slimbus bam instance at 0x17184000 (which has "qcom,num-ees = <2>;").
> 
> Thanks,
> Georgi

-- 
~Vinod