linux-kernel - Re: [PATCH 4/4] remoteproc/davinci: streamline the interrupt management

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Date:   Mon, 26 Jun 2017 11:09:24 -0500
From:   Suman Anna <s-anna@...com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     <linux-remoteproc@...r.kernel.org>, Sekhar Nori <nsekhar@...com>,
        Robert Tivy <rtivy@...com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] remoteproc/davinci: streamline the interrupt
 management

Hi Bjorn,

On 06/25/2017 04:19 PM, Bjorn Andersson wrote:
> On Thu 18 May 15:09 PDT 2017, Suman Anna wrote:
> 
>> The davinci remoteproc driver is currently requesting its interrupt
>> that deals with the virtio kicks in probe, and that too before all
>> the associated variables used by the handler are initialized. This
>> is a lot in advance before the DSP remote processor is even loaded
>> and booted and is not essential. Streamline the interrupt request
>> and freeing operations instead alongside the boot and shutdown of
>> the remote processor.
>>
> 
> I do prefer that all resources are acquired at probe() time, rather than
> handled upon each start/stop. In the current handle_event()
> implementation the remoteproc code will not find the yet unallocated
> notify-id's and do nothing. So this seems okay.
> 
> [..]
>> @@ -213,15 +224,6 @@ static int da8xx_rproc_probe(struct platform_device *pdev)
>>  
>>  	platform_set_drvdata(pdev, rproc);
>>  
>> -	/* everything the ISR needs is now setup, so hook it up */
>> -	ret = devm_request_threaded_irq(dev, irq, da8xx_rproc_callback,
>> -					handle_event, 0, "da8xx-remoteproc",
>> -					rproc);
>> -	if (ret) {
>> -		dev_err(dev, "devm_request_threaded_irq error: %d\n", ret);
>> -		goto free_rproc;
>> -	}
> 
> In the error paths after this the driver will end up freeing the rproc
> context before disabling the irq, so these cases need a call to
> disable_irq().

Hmm, I am not sure I understand why we need disable_irq() when we are
not even requesting it? This is deleting code, not adding. The IRQ
request and free are now balanced in the start and stop ops. The only
call here is a platform_get_irq() which doesn't need any cleanup.

> 
>> -
>>  	/*
>>  	 * rproc_add() can end up enabling the DSP's clk with the DSP
>>  	 * *not* in reset, but da8xx_rproc_start() needs the DSP to be
>> @@ -254,14 +256,6 @@ static int da8xx_rproc_probe(struct platform_device *pdev)
>>  static int da8xx_rproc_remove(struct platform_device *pdev)
>>  {
>>  	struct rproc *rproc = platform_get_drvdata(pdev);
>> -	struct da8xx_rproc *drproc = (struct da8xx_rproc *)rproc->priv;
>> -
>> -	/*
>> -	 * The devm subsystem might end up releasing things before
>> -	 * freeing the irq, thus allowing an interrupt to sneak in while
>> -	 * the device is being removed.  This should prevent that.
>> -	 */
> 
> devres _will not_ disable the IRQ until after remove() returns, making it
> possible for the interrupt handler to be executed after the rproc
> context is freed.
> 
> So this comment would benefit from an update.

Again, this is deleting code, not adding. The remove after this cleanup
will simply be invoking the rproc_del() and rproc_free() call, and
rproc_del() does end up calling the stop since we do use auto-boot where
we free the irq.

regards
Suman

> 
>> -	disable_irq(drproc->irq);
>>  
>>  	rproc_del(rproc);
>>  	rproc_free(rproc);
> 
> Regards,
> Bjorn
>