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Subject: Re: [PATCH] mmc: sdhci: queue work after sdhci_defer_done()
To:     Brian Masney <masneyb@onstation.org>, ulf.hansson@linaro.org
Cc:     faiz_abbas@ti.com, linux-mmc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org
References: <20190524111053.12228-1-masneyb@onstation.org>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
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Message-ID: <70782901-a9ac-5647-1abe-89c86a44a01b@intel.com>
Date:   Fri, 24 May 2019 15:17:13 +0300
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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")
> ---
> See 'sdhci@f98a4900' in qcom-msm8974-lge-nexus5-hammerhead.dts for
> details about how the WiFi is wired into sdhci on this platform.
> 
> bisect log:
> 
>  git bisect start
>  # bad: [4dde821e4296e156d133b98ddc4c45861935a4fb] Merge tag 'xfs-5.2-fixes-1' of git://git.kernel.org/pub/scm/fs/xfs/xfs-linux
>  git bisect bad 4dde821e4296e156d133b98ddc4c45861935a4fb
>  # good: [e93c9c99a629c61837d5a7fc2120cd2b6c70dbdd] Linux 5.1
>  git bisect good e93c9c99a629c61837d5a7fc2120cd2b6c70dbdd
>  # bad: [8c79f4cd441b27df6cadd11b70a50e06b3b3a2bf] Merge tag 'docs-5.2' of git://git.lwn.net/linux
>  git bisect bad 8c79f4cd441b27df6cadd11b70a50e06b3b3a2bf
>  # bad: [67a242223958d628f0ba33283668e3ddd192d057] Merge tag 'for-5.2/block-20190507' of git://git.kernel.dk/linux-block
>  git bisect bad 67a242223958d628f0ba33283668e3ddd192d057
>  # good: [8ff468c29e9a9c3afe9152c10c7b141343270bf3] Merge branch 'x86-fpu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
>  git bisect good 8ff468c29e9a9c3afe9152c10c7b141343270bf3
>  # good: [e2a5be107f52cefb9010ccae6f569c3ddaa954cc] staging: kpc2000: kpc_spi: Fix build error for {read,write}q
>  git bisect good e2a5be107f52cefb9010ccae6f569c3ddaa954cc
>  # bad: [cf482a49af564a3044de3178ea28f10ad5921b38] Merge tag 'driver-core-5.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
>  git bisect bad cf482a49af564a3044de3178ea28f10ad5921b38
>  # good: [9f2e3a53f7ec9ef55e9d01bc29a6285d291c151e] Merge tag 'for-5.2-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
>  git bisect good 9f2e3a53f7ec9ef55e9d01bc29a6285d291c151e
>  # good: [b4b52b881cf08e13d110eac811d4becc0775abbf] Merge tag 'Wimplicit-fallthrough-5.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux
>  git bisect good b4b52b881cf08e13d110eac811d4becc0775abbf
>  # bad: [d5f758f2df8015b8dcf47b6403cc192e4cef734d] mmc: meson-gx: disable HS400
>  git bisect bad d5f758f2df8015b8dcf47b6403cc192e4cef734d
>  # good: [b3fb9d64b497b890f7b779a9f0b40b5cc269ea18] mmc: mmci: define get_dctrl_cfg for legacy variant
>  git bisect good b3fb9d64b497b890f7b779a9f0b40b5cc269ea18
>  # good: [ade024f130f742725da9219624b01666f04bc4a6] memstick: jmb38x_ms: remove set but not used variable 'data'
>  git bisect good ade024f130f742725da9219624b01666f04bc4a6
>  # bad: [42c38d4a1bc41e78dedbf73b0fb35e44007789bb] mmc: core: Fix warning and undefined behavior in mmc voltage handling
>  git bisect bad 42c38d4a1bc41e78dedbf73b0fb35e44007789bb
>  # good: [19d2f695f4e82794df7465b029c02b104d1b9903] mmc: sdhci: Call mmc_request_done() from IRQ handler if possible
>  git bisect good 19d2f695f4e82794df7465b029c02b104d1b9903
>  # bad: [71c733c4e1aeb83e8221e89caeec893d51f88b7b] mmc: tegra: add sdhci tegra suspend and resume
>  git bisect bad 71c733c4e1aeb83e8221e89caeec893d51f88b7b
>  # bad: [c07a48c2651965e84d35cf193dfc0e5f7892d612] mmc: sdhci: Remove finish_tasklet
>  git bisect bad c07a48c2651965e84d35cf193dfc0e5f7892d612
>  # first bad commit: [c07a48c2651965e84d35cf193dfc0e5f7892d612] 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?

>  		} else {
>  			mrqs_done[i] = mrq;
>  			host->mrqs_done[i] = NULL;
>