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

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Date: Fri, 21 Jun 2024 10:47:54 -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

> On Tue, Jun 18, 2024 at 03:52:07PM GMT, Allen Pais wrote:
> > 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'?
>
> All the best,
>
>    Wolfram
>


-- 
       - Allen