Re: [PATCH] ASoC: ti: omap-mcbsp: duplicate sysfs failure after PROBE_DEFER

[David Owens <dowens@precisionplanting.com>]

On 6/14/22 11:08, Mark Brown wrote:
> On Tue, Jun 14, 2022 at 10:59:31AM -0500, David Owens wrote:
>
>> The call to sdma_pcm_platform_register() can return PROBE_DEFER, leading
>> to omap_mcbsp_init() being called multiple times.  sysfs node creation
>> fails in subsequent calls to omap_mcbsp_init(), which prevents
>> the driver from ever successfully probing.  The resulting errors can be
>> seen during boot:
>>
>> [    1.749328] sysfs: cannot create duplicate filename '/devices/platform/68000000.ocp/49022000.mcbsp/max_tx_thres'
>> [    1.759643] CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 5.18.0-yocto-standard #1
>> [    1.767181] Hardware name: Generic OMAP36xx (Flattened Device Tree)
>> [    1.773498] Workqueue: events_unbound deferred_probe_work_func
>> [    1.779449]  unwind_backtrace from show_stack+0x10/0x14
>> [    1.784729]  show_stack from sysfs_warn_dup+0x4c/0x60
> Please think hard before including complete backtraces in upstream
> reports, they are very large and contain almost no useful information
> relative to their size so often obscure the relevant content in your
> message. If part of the backtrace is usefully illustrative (it often is
> for search engines if nothing else) then it's usually better to pull out
> the relevant sections.
Probably just the "sysfs:" line would suffice.  I'll be sure to limit
traces in the future, thanks for the tip.
>> +++ b/sound/soc/ti/omap-mcbsp.c
>> @@ -1403,6 +1403,10 @@ static int asoc_mcbsp_probe(struct platform_device *pdev)
>>          mcbsp->dev = &pdev->dev;
>>          platform_set_drvdata(pdev, mcbsp);
>>
>> +       ret = sdma_pcm_platform_register(&pdev->dev, "tx", "rx");
>> +       if (ret)
>> +               return ret;
>> +
>>          ret = omap_mcbsp_init(pdev);
>>          if (ret)
>>                  return ret;
>> @@ -1412,13 +1416,9 @@ static int asoc_mcbsp_probe(struct platform_device *pdev)
>>                  omap_mcbsp_dai.capture.formats = SNDRV_PCM_FMTBIT_S16_LE;
>>          }
>>
>> -       ret = devm_snd_soc_register_component(&pdev->dev,
>> +       return devm_snd_soc_register_component(&pdev->dev,
>>                                                &omap_mcbsp_component,
>>                                                &omap_mcbsp_dai, 1);
>> -       if (ret)
>> -               return ret;
>> -
>> -       return sdma_pcm_platform_register(&pdev->dev, "tx", "rx");
>>   }
> It's not clear to me how this fixes the problem, your commit message
> doesn't mention how?  I was expecting to see more error handling paths
> being added to unwind the sysfs allocation, or a conversion to devm.  As
> things stand it's not clear to me that the error won't persist in the
> case where we defer registering the component.

Moving sdma_pcm_platform_register() before sysfs node creation allowed
probe to exit with EPROBE_DEFER without needing to unwind sysfs nodes.
While this worked in my particular case, as you point out it might not
address all probe deferrals.  I can look for a more robust solution and
submit as a v2 patch.

-Dave

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