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

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Message-ID: <63609692-ebfc-b0d2-cf7e-b6f591a34e7e@quicinc.com>
Date: Thu, 23 Jan 2025 17:38:15 +0530
From: Md Sadre Alam <quic_mdalam@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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 1/21/2025 4:24 PM, Dmitry Baryshkov wrote:
> 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...'
Ok
> 
>> 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.
Ok
> 
>> 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.
Sure , will fix this in next revision.
> 
>>
>> 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?
This revision register we need only to differentiate b/w BAM-Lite and
BAM-NDP. if num_ees != 0 then no need read this revision register.
The SOCs which is having BAM-NDP and BAM-Lite having 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
>>
>