linux-kernel - Re: [PATCH v3] dmaengine: qcom: bam_dma: Avoid writing unavailable register

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Message-ID: <5d27eea0-56cd-4961-9fd5-f2398a24f958@quicinc.com>
Date: Mon, 9 Dec 2024 16:05:22 +0530
From: Manikanta Mylavarapu <quic_mmanikan@...cinc.com>
To: Md Sadre Alam <quic_mdalam@...cinc.com>, <vkoul@...nel.org>,
        <martin.petersen@...cle.com>, <ulf.hansson@...aro.org>,
        <av2082000@...il.com>, <linux-arm-msm@...r.kernel.org>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <uic_mdalam@...cinc.com>, <quic_srichara@...cinc.com>,
        <quic_varada@...cinc.com>
Subject: Re: [PATCH v3] dmaengine: qcom: bam_dma: Avoid writing unavailable
 register



On 12/9/2024 1:01 PM, 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>
> ---
> 
> Change in [v3]
> 
> * Removed BAM_LITE macro
> 
> * Updated commit message
> 
> * Adjusted if condition check
> 
> * Renamed BAM-NDP macro to BAM_NDP_REVISION_START and 
>   BAM_NDP_REVISION_END
> 
> Change in [v2]
> 
> * Replace 0xff with REVISION_MASK in the statement
>   bdev->bam_revision = val & REVISION_MASK
> 
> Change in [v1]
> 
> * Added initial patch
> 
>  drivers/dma/qcom/bam_dma.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> index d43a881e43b9..a00dd0331ff5 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_NDP_REVISION_START	0x20
> +#define BAM_NDP_REVISION_END	0x27
> +
>  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 +445,10 @@ 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_NDP_REVISION_START &&
> +	    bdev->bam_revision <= BAM_NDP_REVISION_END)

Please use in_range().

> +		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 +1006,10 @@ 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_NDP_REVISION_START &&
> +		    bdev->bam_revision <= BAM_NDP_REVISION_END)

Please use in_range().

Thanks & Regards,
Manikanta.