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

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Message-ID: <43d86040-ff8e-4c48-9163-e9a2648e1f91@quicinc.com>
Date: Fri, 10 Jan 2025 10:51:48 +0530
From: Md Sadre Alam <quic_mdalam@...cinc.com>
To: Georgi Djakov <djakov@...nel.org>, <vkoul@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <dmaengine@...r.kernel.org>
CC: <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 1/8/2025 3:00 AM, 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.
> 
> [..]
> 
>>       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>;").
I have posted the fix. Patch available at [1]
[1] 
https://patchwork.kernel.org/project/linux-arm-msm/patch/20250110051409.4099727-1-quic_mdalam@quicinc.com/

Please check once.

Thanks,
Alam.