linux-kernel - Re: [PATCH v3] dmaengine: qcom: bam_dma: Fix BAM

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Message-ID: <okiy7n5nvjadbfczmnn2eoxwe36ilug5xutben3rg2nkvpehb5@kr2t4hvidaht>
Date: Tue, 21 Jan 2025 12:54:56 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Md Sadre Alam <quic_mdalam@...cinc.com>
Cc: vkoul@...nel.org, kees@...nel.org, fenghua.yu@...el.com, 
	linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, 
	djakov@...nel.org, quic_srichara@...cinc.com, quic_varada@...cinc.com
Subject: Re: [PATCH v3] dmaengine: qcom: bam_dma: Fix BAM_RIVISON register
 handling

On Tue, Jan 21, 2025 at 02:42:41PM +0530, Md Sadre Alam wrote:
> This patch resolves a bug from the previous commit where the

Please check Documentation/process/submitting-patches.rst, 'This
patch...'

> BAM_DESC_CNT_TRSHLD register was conditionally written based on BAM-NDP
> mode. The issue was reading the BAM_REVISION register hanging if num-ees

First start with the issue description, then proceed to the changes
description.

> was not zero, which occurs when the SoCs power on BAM remotely. So the
> BAM_REVISION register read has been moved to inside if condition.

Imperative language, please. While we are at it, please also fix commit
subject.

> 
> Fixes: 57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing unavailable register")
> Reported-by: Georgi Djakov <djakov@...nel.org>
> Link: https://lore.kernel.org/lkml/9ef3daa8-cdb1-49f2-8d19-a72d6210ff3a@kernel.org/
> Signed-off-by: Md Sadre Alam <quic_mdalam@...cinc.com>
> ---
> 
> Change in [v3]
> 
> * Revised commit details
> 
> Change in [v2]
> 
> * Removed unnecessary if checks.
> * Relocated the BAM_REVISION register read within the if condition.
> 
> Change in [v1]
> 
> * https://lore.kernel.org/lkml/1a5fc7e9-39fe-e527-efc3-1ea990bbb53b@quicinc.com/
> * Posted initial fixup for BAM revision register read handling
>  drivers/dma/qcom/bam_dma.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> index c14557efd577..d227b4f5b6b9 100644
> --- a/drivers/dma/qcom/bam_dma.c
> +++ b/drivers/dma/qcom/bam_dma.c
> @@ -1199,11 +1199,11 @@ static int bam_init(struct bam_device *bdev)
>  	u32 val;
>  
>  	/* read revision and configuration information */

Please extend the comment, mentioning why the register is read only in
!num_ees case. BTW: how do we get revision if num_ees != 0?

> -	val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
> -	if (!bdev->num_ees)
> +	if (!bdev->num_ees) {
> +		val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION));
>  		bdev->num_ees = (val >> NUM_EES_SHIFT) & NUM_EES_MASK;
> -
> -	bdev->bam_revision = val & REVISION_MASK;
> +		bdev->bam_revision = val & REVISION_MASK;
> +	}
>  
>  	/* check that configured EE is within range */
>  	if (bdev->ee >= bdev->num_ees)
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry