linux-kernel - Re: [PATCH] rpmsg: qcom_smd: Access APCS through mailbox framework

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Date:   Wed, 6 Dec 2017 11:54:27 -0800
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jitendra Sharma <shajit@...eaurora.org>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] rpmsg: qcom_smd: Access APCS through mailbox framework

On 12/06/2017 11:02 AM, Bjorn Andersson wrote:
> On Wed 06 Dec 04:08 PST 2017, Jitendra Sharma wrote:
>
>> Hi Bjorn,
>>
> Hi Jitendra,
>
>> On 11/16/2017 12:38 PM, Bjorn Andersson wrote:
> [..]
>>> @@ -365,7 +371,12 @@ static void qcom_smd_signal_channel(struct qcom_smd_channel *channel)
>>>   {
>>>   	struct qcom_smd_edge *edge = channel->edge;
>>> -	regmap_write(edge->ipc_regmap, edge->ipc_offset, BIT(edge->ipc_bit));
>>> +	if (edge->mbox_chan) {
>>> +		mbox_send_message(edge->mbox_chan, NULL);
>> mbox_send_message could fail. So return value should be checked
> qcom_apcs_ipc_send_data() can't fail, so the case when
> mbox_send_message() would fail is if more than MBOX_TX_QUEUE_LEN (20)
> callers that has managed to put their data in the queue but not yet
> execute msg_submit().
>
> As each bit in the APCS IPC register is modelled as it's own mailbox
> channel this error case would mean that as mbox_send_message() returns
> with an error there will soon be 20 callers entering
> qcom_apcs_ipc_send_data() and trigger this very bit.
>
>
> When this happens mbox_send_message() will print an error in the log, so
> there's no point in having the caller also print an error.
>
> When it comes to dealing with a failing call to mbox_send_message() we
> have already posted the message in the FIFO, so we have no way to abort
> the transmission, as such the only way to deal with this is to either
> retry or ignore the problem; and the mailbox queue will ensure that we
> retry 20 times.
>

Maybe you should wrap this up into a comment in the code? Then we don't
have to dig this out of the mail list archives to figure out why we
aren't checking for an error.

-- 
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