linux-kernel - Re: [PATCH v3] mmc: Convert from tasklet to BH workqueue

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Date: Fri, 21 Jun 2024 11:35:40 -0700
From: Allen <allen.lkml@...il.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>, Allen Pais <allen.lkml@...il.com>, 
	Aubin Constans <aubin.constans@...rochip.com>, Ulf Hansson <ulf.hansson@...aro.org>, 
	Nicolas Ferre <nicolas.ferre@...rochip.com>, 
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Claudiu Beznea <claudiu.beznea@...on.dev>, 
	Manuel Lauss <manuel.lauss@...il.com>, Michał Mirosław <mirq-linux@...e.qmqm.pl>, 
	Jaehoon Chung <jh80.chung@...sung.com>, Aaro Koskinen <aaro.koskinen@....fi>, 
	Adrian Hunter <adrian.hunter@...el.com>, Florian Fainelli <florian.fainelli@...adcom.com>, 
	Ray Jui <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, Alex Dubov <oakad@...oo.com>, 
	Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Bruce Chang <brucechang@....com.tw>, Harald Welte <HaraldWelte@...tech.com>, 
	Pierre Ossman <pierre@...man.eu>, Christian Loehle <christian.loehle@....com>, linux-mmc@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-omap@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v3] mmc: Convert from tasklet to BH workqueue

> > > The only generic interface to execute asynchronously in the BH context is
> > > tasklet; however, it's marked deprecated and has some design flaws. To
> > > replace tasklets, BH workqueue support was recently added. A BH workqueue
> > > behaves similarly to regular workqueues except that the queued work items
> > > are executed in the BH context.
> > >
> > > This patch converts drivers/mmc/* from tasklet to BH workqueue.
> > >
> > > Based on the work done by Tejun Heo <tj@...nel.org>
> >
> > Has this been fully build-tested?
> >
> > ===
> > drivers/mmc/host/renesas_sdhi_internal_dmac.c: In function ‘renesas_sdhi_internal_dmac_complete_work_fn’:
> > ./include/linux/container_of.h:20:54: error: ‘struct tmio_mmc_host’ has no member named ‘dma_complete’
> > ===
>
>  Yes, it does break. My bad, my local compile testing failed to catch this.
>
> >
> > In deed, 'dma_complete' is only in 'struct renesas_sdhi_dma'. From
> > there, we can get to the parent 'struct renesas_sdhi' using
> > container_of. But then, I don't see a way to go to 'struct
> > tmio_mmc_host' from there. The other way around is possible because
> > there is the pointer 'struct tmio_mmc_data *pdata' in the TMIO struct
> > pointing to the data contained in 'struct renesas_sdhi'. 'host_to_priv()'
> > does the math. But I don't see a path the other way around.
> >
>
>  I have been looking at this code since the issue was reported. Yes it
> is a bit tricky and so far, the only way I found was to introduce a new pointer.
> But, I am not very familiar with the code and have asked Ulf for pointers.
>
> If introducing the pointer is the only way forward and is an
> acceptable solution,
> I can send out a draft.
>
> Thanks,
> Allen
>
> > So, it doesn't look like the workqueue interface can provide a
> > generic pointer like tasklets could do? This means we have to add a
> > pointer from 'struct renesas_sdhi' to 'struct tmio_mmc_host'?
> >


How about the following?

diff --git a/drivers/mmc/host/renesas_sdhi_internal_dmac.c
b/drivers/mmc/host/renesas_sdhi_internal_dmac.c
index 5fd276492f80..9a63b78837e2 100644
--- a/drivers/mmc/host/renesas_sdhi_internal_dmac.c
+++ b/drivers/mmc/host/renesas_sdhi_internal_dmac.c
@@ -484,9 +484,14 @@ static bool
renesas_sdhi_internal_dmac_complete(struct tmio_mmc_host *host)
        return true;
 }

-static void renesas_sdhi_internal_dmac_complete_work_fn(struct work_struct *t)
+static void renesas_sdhi_internal_dmac_complete_work_fn(struct
work_struct *work)
 {
-       struct tmio_mmc_host *host = from_work(host, t, dma_complete);
+       struct renesas_sdhi_dma *dma_priv = container_of(work,
+                                                        struct
renesas_sdhi_dma,
+                                                        dma_complete);
+       struct renesas_sdhi *sdhi = container_of(dma_priv,
+                                                struct renesas_sdhi, dma_priv);
+       struct tmio_mmc_host *host = sdhi->mmc_data->host;

        spin_lock_irq(&host->lock);
        if (!renesas_sdhi_internal_dmac_complete(host))
diff --git a/include/linux/mfd/tmio.h b/include/linux/mfd/tmio.h
index eace8ea6cda0..cf2cca0e96b5 100644
--- a/include/linux/mfd/tmio.h
+++ b/include/linux/mfd/tmio.h
@@ -100,6 +100,7 @@ struct tmio_mmc_data {
        dma_addr_t                      dma_rx_offset;
        unsigned int                    max_blk_count;
        unsigned short                  max_segs;
+       struct tmio_mmc_host            *host;          /* back
pointer to the parent struct */
        void (*set_pwr)(struct platform_device *host, int state);
        void (*set_clk_div)(struct platform_device *host, int state);
 };

Thanks.