linux-kernel - Re: [PATCH v5 2/5] firmware: encapsulate firmware loading status

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Date:   Wed, 19 Oct 2016 10:05:49 +0200
From:   Daniel Wagner <daniel.wagner@...-carit.de>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
CC:     Daniel Wagner <wagi@...om.org>, <linux-kernel@...r.kernel.org>,
        Ming Lei <ming.lei@...onical.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Srivatsa S . Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
        "Rafael J . Wysocki" <rjw@...k.pl>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Takashi Iwai <tiwai@...e.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Arend van Spriel <arend.vanspriel@...adcom.com>
Subject: Re: [PATCH v5 2/5] firmware: encapsulate firmware loading status

On 10/18/2016 11:54 PM, Luis R. Rodriguez wrote:
> On Tue, Oct 18, 2016 at 03:30:45PM +0200, Daniel Wagner wrote:
>> On 10/10/2016 10:37 PM, Luis R. Rodriguez wrote:
>>
>>>>   fw_get_fileystem_firmware()
>>>>     fw_finish_direct_load()
>>>>       complete_all()
>>>>
>>>>
>>>> 2nd request (waiter context)
>>>>
>>>> _request_firmware()
>>>>   _request_firmware_prepare()
>>>>      fw_lookup_allocate_buf()      # finds previously allocated buf
>>>>                                    # returns 1 -> wait for loading
>>>>      sync_cached_firmware_buf()
>>>>         wait_for_completion_interruptible_timeout()
>>>
>>> No, that's wait_for_completion_interruptible() not
>>>            wait_for_completion_interruptible_timeout()
>>
>> I confused that one from _request_firmware_load().
> 
> Right and wait_for_completion_interruptible() has no timeout.

All wait_for_completion_*() function are small wrappers around
a common implemention. I thought that would be a clever idea to
reuse here, but from our discussion I see it isn't. My bad.

static int fw_umh_wait_timeout(struct fw_umh *fw_umh, long timeout)
{
	int ret;

	ret = wait_for_completion_interruptible_timeout(&fw_umh->completion,
							timeout);
	if (ret != 0 && test_bit(FW_UMH_ABORTED, &fw_umh->status))
		return -ENOENT;

	return ret;
}


long __sched
wait_for_completion_interruptible_timeout(struct completion *x,
					  unsigned long timeout)
{
	return wait_for_common(x, timeout, TASK_INTERRUPTIBLE);
}

int __sched wait_for_completion_interruptible(struct completion *x)
{
	long t = wait_for_common(x, MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE);
	if (t == -ERESTARTSYS)
		return t;
	return 0;
}


I think it is far better to do something like:

static __fw_umh_wait_common(struct fw_umh *fw_umh, long timeout) { ... }

#define fw_umh_wait(fw_umh) __fw_umh_wait_common(fw_umh, MAX_SCHEDULE_TIMEOUT)
#define fw_umh_wait_timeout(fw_umh, timeout) __fw_umh_wait_common(fw_umh, timeout)

(The function prefixes will be different, since umh isn't right as discussed.)

>>> Also note that we only call sync_cached_firmware_buf()
>>> *iff* fw_lookup_and_allocate_buf() returned the 1 -- I mentioned
>>> when this happens above. That happens only if we already had the entry on
>>> the fw cache. As it stands -- concurrent calls against the same fw name
>>> could cause a clash here, as such, the wait_for_completion_interruptible()
>>> is indeed still needed.
>>>
>>> Further optimizations can be considered later but for indeed, agreed
>>> that completion is needed even for the direct fw load case. The timeout
>>> though, I don't see a reason for it.
>>
>> So I think I found the source of the confusion about fw_umh_wait_timeout().
>> When providing a timeout value of 0 you get the
>> wait_for_completion_interruptible() version.
> 
> I fail to see that, how so? Note that 0 does is not allowed anyway:
> 
> static inline long firmware_loading_timeout(void)
> {
>         return loading_timeout > 0 ? loading_timeout * HZ : MAX_JIFFY_OFFSET;
> }

Correct. The fw_umh_wait_timeout(0) is hard coded in sync_cached_firmware_buf().
fw_umh_wait_timeout(fw_umh, firmware_loading_timeout()) is used
_request_firmware_load().

I'll update the series and hopefully we get this all sorted out in the new
version. 

cheers,
daniel