Re: [PATCH] dmaengine: qcom-bam: fix circular buffer handling

Sricharan R
2019-06-19T17:50:23Z

Hi Srini,

On 6/18/2019 10:20 PM, Srinivas Kandagatla wrote:
>
>
> On 18/06/2019 17:27, Sricharan R wrote:
>>   The Macro's expect that buffer size is power of 2. So we are infact passing the actual correct
>>   size ( MAX_DESCRIPTORS + 1 = 4096)
> This will make the circular buffer macros happy but question is that do we actually have that many descriptor buffers?
>
> This is what is in the driver:
>
> #define BAM_DESC_FIFO_SIZE    SZ_32K
> #define MAX_DESCRIPTORS (BAM_DESC_FIFO_SIZE / sizeof(struct bam_desc_hw) - 1)
> #define BAM_FIFO_SIZE    (SZ_32K - 8)
>
> Wouldn't having MAX_DESCRIPTORS + 1 = 4096  lead to overflow the actual descriptor memory size of (SZ_32K - 8) ?
>

Right, but the CIRC_SPACE macro assumes there is 1 space less than the actual size.
That said, agree there is an issue on the boundary. I will also do some testing tomorrow
on this and get back.

Regards,
Sricharan
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