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

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Message-ID: <31574ef2-d675-bb36-08d1-18b756ebd29e@linaro.org>
Date:   Tue, 18 Jun 2019 17:50:06 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Sricharan R <sricharan@...eaurora.org>, vkoul@...nel.org
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] dmaengine: qcom-bam: fix circular buffer handling



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) ?

--srini