linux-kernel - Re: [PATCH v2] soundwire: qcom: wait for fifo space to be available before read/write

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Date:   Thu, 1 Apr 2021 17:49:46 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        vkoul@...nel.org
Cc:     robh@...nel.org, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        sanyog.r.kale@...el.com, yung-chuan.liao@...ux.intel.com
Subject: Re: [PATCH v2] soundwire: qcom: wait for fifo space to be available
 before read/write



On 01/04/2021 15:36, Pierre-Louis Bossart wrote:
> 
> 
> On 4/1/21 4:00 AM, Srinivas Kandagatla wrote:
>> If we write registers very fast we can endup in a situation where some
>> of the writes will be dropped without any notice.
>>
>> So wait for the fifo space to be available before reading/writing the
>> soundwire registers.
> 
> Out of curiosity, do you actually need to do a check in the read case as 
> well?

Yes, This is just to make sure the read command is finished and fifo is 
ready with data.

If not we will be reading quickly an empty fifo!

> 
> The commit message talks about writes getting dropped, is the opposite 
> also a problem?

Its highly likely, for safety I have added support for both write and 
read waits in this patch.


--srini
>