linux-kernel - Re: [PATCH] remoteproc: stm32: fix mbox_send

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Date:   Fri, 28 May 2021 10:03:39 +0200
From:   Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Ohad Ben-Cohen <ohad@...ery.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        <linux-remoteproc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH] remoteproc: stm32: fix mbox_send_message call

Hello Bjorn,

On 5/28/21 5:26 AM, Bjorn Andersson wrote:
> On Tue 20 Apr 04:19 CDT 2021, Arnaud Pouliquen wrote:
> 
>> mbox_send_message is called by passing a local dummy message or
>> a function parameter. As the message is queued, it is dereferenced.
>> This works because the message field is not used by the stm32 ipcc
>> driver, but it is not clean.
>>
>> Fix by passing a constant string in all cases.
>>
>> The associated comments are removed because rproc should not have to
>> deal with the behavior of the mailbox frame.
>>
> 
> Didn't we conclude that the mailbox driver doesn't actually dereference
> the pointer being passed?

Right it can store the reference to queue the sent.

> 
> If so I would prefer that you just pass NULL, so that if you in the
> future need to pass some actual data it will be easy to distinguish the
> old and new case.

I can not use NULL pointer in stm32_rproc_attach and stm32_rproc_detach case.
The reason is that the tx_done callback is not called if the message is NULL.
(https://elixir.bootlin.com/linux/latest/source/drivers/mailbox/mailbox.c#L106)

I could use NULL pointer in stm32_rproc_kick, but I would prefer to use the same way
of calling mbox_send_message for all use cases and not take into account the
mailbox internal behavior.

Thanks,
Arnaud


> 
> Regards,
> Bjorn
> 
>> Reported-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
>> ---
>>  drivers/remoteproc/stm32_rproc.c | 14 +++++---------
>>  1 file changed, 5 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/remoteproc/stm32_rproc.c b/drivers/remoteproc/stm32_rproc.c
>> index 7353f9e7e7af..0e8203a432ab 100644
>> --- a/drivers/remoteproc/stm32_rproc.c
>> +++ b/drivers/remoteproc/stm32_rproc.c
>> @@ -474,14 +474,12 @@ static int stm32_rproc_attach(struct rproc *rproc)
>>  static int stm32_rproc_detach(struct rproc *rproc)
>>  {
>>  	struct stm32_rproc *ddata = rproc->priv;
>> -	int err, dummy_data, idx;
>> +	int err, idx;
>>  
>>  	/* Inform the remote processor of the detach */
>>  	idx = stm32_rproc_mbox_idx(rproc, STM32_MBX_DETACH);
>>  	if (idx >= 0 && ddata->mb[idx].chan) {
>> -		/* A dummy data is sent to allow to block on transmit */
>> -		err = mbox_send_message(ddata->mb[idx].chan,
>> -					&dummy_data);
>> +		err = mbox_send_message(ddata->mb[idx].chan, "stop");
>>  		if (err < 0)
>>  			dev_warn(&rproc->dev, "warning: remote FW detach without ack\n");
>>  	}
>> @@ -493,15 +491,13 @@ static int stm32_rproc_detach(struct rproc *rproc)
>>  static int stm32_rproc_stop(struct rproc *rproc)
>>  {
>>  	struct stm32_rproc *ddata = rproc->priv;
>> -	int err, dummy_data, idx;
>> +	int err, idx;
>>  
>>  	/* request shutdown of the remote processor */
>>  	if (rproc->state != RPROC_OFFLINE) {
>>  		idx = stm32_rproc_mbox_idx(rproc, STM32_MBX_SHUTDOWN);
>>  		if (idx >= 0 && ddata->mb[idx].chan) {
>> -			/* a dummy data is sent to allow to block on transmit */
>> -			err = mbox_send_message(ddata->mb[idx].chan,
>> -						&dummy_data);
>> +			err = mbox_send_message(ddata->mb[idx].chan, "detach");
>>  			if (err < 0)
>>  				dev_warn(&rproc->dev, "warning: remote FW shutdown without ack\n");
>>  		}
>> @@ -556,7 +552,7 @@ static void stm32_rproc_kick(struct rproc *rproc, int vqid)
>>  			continue;
>>  		if (!ddata->mb[i].chan)
>>  			return;
>> -		err = mbox_send_message(ddata->mb[i].chan, (void *)(long)vqid);
>> +		err = mbox_send_message(ddata->mb[i].chan, "kick");
>>  		if (err < 0)
>>  			dev_err(&rproc->dev, "%s: failed (%s, err:%d)\n",
>>  				__func__, ddata->mb[i].name, err);
>> -- 
>> 2.17.1
>>