Message-ID: <f956351e-de37-062b-c02e-5cbdf9a3bdfd@linux.intel.com>
Date:   Thu, 9 Feb 2023 10:33:50 -0600
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Subject: Re: [PATCH 3/5] soundwire: qcom: wait for fifo to be empty before
 suspend
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To:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        vkoul@kernel.org
Cc:     yung-chuan.liao@linux.intel.com, alsa-devel@alsa-project.org,
        linux-kernel@vger.kernel.org, steev@kali.org,
        johan+linaro@kernel.org, quic_bjorande@quicinc.com
References: <20230209131336.18252-1-srinivas.kandagatla@linaro.org>
 <20230209131336.18252-4-srinivas.kandagatla@linaro.org>
 <dbec6aab-6456-72b3-39b6-3490dfdf083c@linux.intel.com>
 <a1d79008-3ec4-d7b5-12b5-ea5c6c5a8370@linaro.org>
From:   Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
In-Reply-To: <a1d79008-3ec4-d7b5-12b5-ea5c6c5a8370@linaro.org>
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On 2/9/23 09:52, Srinivas Kandagatla wrote:
> 
> 
> On 09/02/2023 15:23, Pierre-Louis Bossart wrote:
>>
>>
>> On 2/9/23 07:13, Srinivas Kandagatla wrote:
>>> Wait for Fifo to be empty before going to suspend or before bank
>>> switch happens. Just to make sure that all the reads/writes are done.
>>
>> For the suspend case that seems like a valid approach, but for bank
>> switch don't we already have a bus->msg_lock mutex that will prevent the
>> bank switch command from being sent before the other commands are
>> handled?
> 
> All read/writes are fifo based, so writes could be still pending.

I am not following. The bank switch happens with this function, where a
mutex is taken.

int sdw_transfer(struct sdw_bus *bus, struct sdw_msg *msg)
{
	int ret;

	mutex_lock(&bus->msg_lock);

	ret = sdw_transfer_unlocked(bus, msg);

	mutex_unlock(&bus->msg_lock);

	return ret;
}

The transfer_unlocked is synchronous and waits for the command response
to be available.

In other words, there's both a mutual exclusion and a synchronous
behavior, so not sure how commands *before* the bank switch could be
pending?