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

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Message-ID: <b874e1fc-2d0d-f18b-3ebc-6ebff2e02e8f@quicinc.com>
Date: Tue, 26 Nov 2024 10:27:13 +0530
From: Md Sadre Alam <quic_mdalam@...cinc.com>
To: Varadarajan Narayanan <quic_varada@...cinc.com>
CC: <vkoul@...nel.org>, <ulf.hansson@...aro.org>, <martin.petersen@...cle.com>,
        <kees@...nel.org>, <dave.jiang@...el.com>, <av2082000@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_srichara@...cinc.com>
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Avoid writing unavailable
 register



On 11/23/2024 10:06 AM, Varadarajan Narayanan wrote:
> On Fri, Nov 22, 2024 at 12:46:49PM +0530, 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 avoid writing
>> this register for clients who is using BAM-Lite mode.
>>
>> Signed-off-by: Md Sadre Alam <quic_mdalam@...cinc.com>
>> ---
>>   drivers/dma/qcom/bam_dma.c | 22 ++++++++++++++--------
>>   1 file changed, 14 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
>> index d43a881e43b9..13a08c03746b 100644
>> --- a/drivers/dma/qcom/bam_dma.c
>> +++ b/drivers/dma/qcom/bam_dma.c
>> @@ -59,6 +59,9 @@ struct bam_desc_hw {
>>   #define DESC_FLAG_NWD BIT(12)
>>   #define DESC_FLAG_CMD BIT(11)
>>
>> +#define BAM_LITE	0x13
>> +#define BAM_NDP		0x20
>> +
>>   struct bam_async_desc {
>>   	struct virt_dma_desc vd;
>>
>> @@ -398,6 +401,7 @@ struct bam_device {
>>
>>   	/* dma start transaction tasklet */
>>   	struct tasklet_struct task;
>> +	u32 bam_revision;
>>   };
>>
>>   /**
>> @@ -441,8 +445,9 @@ static void bam_reset(struct bam_device *bdev)
>>   	writel_relaxed(val, bam_addr(bdev, 0, BAM_CTRL));
>>
>>   	/* set descriptor threshold, start with 4 bytes */
>> -	writel_relaxed(DEFAULT_CNT_THRSHLD,
>> -			bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
>> +	if (bdev->bam_revision >= BAM_LITE && bdev->bam_revision < BAM_NDP)
>> +		writel_relaxed(DEFAULT_CNT_THRSHLD,
>> +			       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
>>
>>   	/* Enable default set of h/w workarounds, ie all except BAM_FULL_PIPE */
>>   	writel_relaxed(BAM_CNFG_BITS_DEFAULT, bam_addr(bdev, 0, BAM_CNFG_BITS));
>> @@ -1000,9 +1005,9 @@ static void bam_apply_new_config(struct bam_chan *bchan,
>>   			maxburst = bchan->slave.src_maxburst;
>>   		else
>>   			maxburst = bchan->slave.dst_maxburst;
>> -
>> -		writel_relaxed(maxburst,
>> -			       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
>> +		if (bdev->bam_revision >= BAM_LITE && bdev->bam_revision < BAM_NDP)
>> +			writel_relaxed(maxburst,
>> +				       bam_addr(bdev, 0, BAM_DESC_CNT_TRSHLD));
>>   	}
>>
>>   	bchan->reconfigure = 0;
>> @@ -1192,10 +1197,11 @@ 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 & 0xff;
> 
> Use REVISION_MASK instead of 0xff
Ok
> 
> -Varada
> 
>>   	/* check that configured EE is within range */
>>   	if (bdev->ee >= bdev->num_ees)
>> --
>> 2.34.1
>>