netdev - Re: [net-next v4 10/12] ASoC: SOF: Introduce descriptors for SOF client

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Date:   Fri, 22 May 2020 13:35:54 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        davem@...emloft.net, gregkh@...uxfoundation.org,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        nhorman@...hat.com, sassmann@...hat.com,
        Fred Oh <fred.oh@...ux.intel.com>
Subject: Re: [net-next v4 10/12] ASoC: SOF: Introduce descriptors for SOF
 client



On 5/22/20 12:10 PM, Jason Gunthorpe wrote:
> On Fri, May 22, 2020 at 10:33:20AM -0500, Pierre-Louis Bossart wrote:
> 
>>> Maybe not great, but at least it is consistent with all the lifetime
>>> models and the operation of the driver core.
>>
>> I agree your comments are valid ones, I just don't have a solution to be
>> fully compliant with these models and report failures of the driver probe
>> for a child device due to configuration issues (bad audio topology, etc).
> 
> 
>> My understanding is that errors on probe are explicitly not handled in the
>> driver core, see e.g. comments such as:
> 
> Yes, but that doesn't really apply here...
>   
>> /*
>>   * Ignore errors returned by ->probe so that the next driver can try
>>   * its luck.
>>   */
>> https://elixir.bootlin.com/linux/latest/source/drivers/base/dd.c#L636
>>
>> If somehow we could request the error to be reported then probably we
>> wouldn't need this complete/wait_for_completion mechanism as a custom
>> notification.
> 
> That is the same issue as the completion, a driver should not be
> making assumptions about ordering like this. For instance what if the
> current driver is in the initrd and the 2nd driver is in a module in
> the filesystem? It will not probe until the system boots more
> completely.
> 
> This is all stuff that is supposed to work properly.
> 
>> Not at the moment, no. there are no failures reported in dmesg, and
>> the user does not see any card created. This is a silent error.
> 
> Creating a partial non-function card until all the parts are loaded
> seems like the right way to surface an error like this.
> 
> Or don't break the driver up in this manner if all the parts are really
> required just for it to function - quite strange place to get into.

This is not about having all the parts available - that's handled 
already with deferred probe - but an error happening during card 
registration. In that case the ALSA/ASoC core throws an error and we 
cannot report it back to the parent.

> What happens if the user unplugs this sub driver once things start
> running?

refcounting in the ALSA core prevents that from happening usually.