Re: Issue with Broadcom wireless in 5.2rc1 (was Re: [PATCH] mmc: sdhci: queue work after sdhci_defer_done())

From: Adrian Hunter <adrian.hunter@intel.com>
To: Brian Masney <masneyb@onstation.org>,
	Arend Van Spriel <arend.vanspriel@broadcom.com>
Cc: Franky Lin <franky.lin@broadcom.com>,
	Hante Meuleman <hante.meuleman@broadcom.com>,
	Chi-Hsien Lin <chi-hsien.lin@cypress.com>,
	Wright Feng <wright.feng@cypress.com>,
	ulf.hansson@linaro.org, faiz_abbas@ti.com,
	linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-msm@vger.kernel.org, Kalle Valo <kvalo@codeaurora.org>,
	linux-wireless@vger.kernel.org,
	brcm80211-dev-list.pdl@broadcom.com,
	brcm80211-dev-list@cypress.com, netdev@vger.kernel.org
Subject: Re: Issue with Broadcom wireless in 5.2rc1 (was Re: [PATCH] mmc: sdhci: queue work after sdhci_defer_done())
Date: Mon, 27 May 2019 10:48:24 +0300	[thread overview]
Message-ID: <e7818bf9-a1d1-24b8-360d-62d7493afa91@intel.com> (raw)
In-Reply-To: <20190526195819.GA29665@basecamp>

On 26/05/19 10:58 PM, Brian Masney wrote:
> On Sun, May 26, 2019 at 08:42:21PM +0200, Arend Van Spriel wrote:
>> On 5/26/2019 2:21 PM, Brian Masney wrote:
>>> + Broadcom wireless maintainers
>>>
>>> On Fri, May 24, 2019 at 11:49:58AM -0400, Brian Masney wrote:
>>>> On Fri, May 24, 2019 at 03:17:13PM +0300, Adrian Hunter wrote:
>>>>> On 24/05/19 2:10 PM, Brian Masney wrote:
>>>>>> WiFi stopped working on the LG Nexus 5 phone and the issue was bisected
>>>>>> to the commit c07a48c26519 ("mmc: sdhci: Remove finish_tasklet") that
>>>>>> moved from using a tasklet to a work queue. That patch also changed
>>>>>> sdhci_irq() to return IRQ_WAKE_THREAD instead of finishing the work when
>>>>>> sdhci_defer_done() is true. Change it to queue work to the complete work
>>>>>> queue if sdhci_defer_done() is true so that the functionality is
>>>>>> equilivent to what was there when the finish_tasklet was present. This
>>>>>> corrects the WiFi breakage on the Nexus 5 phone.
>>>>>>
>>>>>> Signed-off-by: Brian Masney <masneyb@onstation.org>
>>>>>> Fixes: c07a48c26519 ("mmc: sdhci: Remove finish_tasklet")
>>>>>> ---
>>>>>> [ ... ]
>>>>>>
>>>>>>   drivers/mmc/host/sdhci.c | 2 +-
>>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>>>>> index 97158344b862..3563c3bc57c9 100644
>>>>>> --- a/drivers/mmc/host/sdhci.c
>>>>>> +++ b/drivers/mmc/host/sdhci.c
>>>>>> @@ -3115,7 +3115,7 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
>>>>>>   			continue;
>>>>>>   		if (sdhci_defer_done(host, mrq)) {
>>>>>> -			result = IRQ_WAKE_THREAD;
>>>>>> +			queue_work(host->complete_wq, &host->complete_work);
>>>>>
>>>>> The IRQ thread has a lot less latency than the work queue, which is why it
>>>>> is done that way.
>>>>>
>>>>> I am not sure why you say this change is equivalent to what was there
>>>>> before, nor why it fixes your problem.
>>>>>
>>>>> Can you explain some more?
>>>>
>>>> [ ... ]
>>>>
>>>> drivers/net/wireless/broadcom/brcm80211/brcmfmac/sdio.c calls
>>>> sdio_claim_host() and it appears to never return.

This is because SDHCI is using the IRQ thread to process the SDIO card
interrupt (sdio_run_irqs()).  When the card driver tries to use the card, it
causes interrupts which deadlocks since c07a48c26519 ("mmc: sdhci: Remove
finish_tasklet") has moved the tasklet processing to the IRQ thread.

I would expect to be able to use the IRQ thread to complete requests, and it
is desirable to do so because it is lower latency.

Probably, SDHCI should use sdio_signal_irq() which queues a work item, and
is what other drivers are doing.

I will investigate some more and send a patch.