linux-kernel - Re: [PATCH v2 1/3] spi: spi-mem: add automatic poll status functions

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Message-ID: <20210510112249.5613978e@collabora.com>
Date:   Mon, 10 May 2021 11:22:49 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Patrice CHOTARD <patrice.chotard@...s.st.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        <linux-spi@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <christophe.kerello@...s.st.com>
Subject: Re: [PATCH v2 1/3] spi: spi-mem: add automatic poll status
 functions

On Mon, 10 May 2021 10:46:48 +0200
Patrice CHOTARD <patrice.chotard@...s.st.com> wrote:

> >   
> >> +
> >> +	if (ctlr->mem_ops && ctlr->mem_ops->poll_status) {
> >> +		ret = spi_mem_access_start(mem);
> >> +		if (ret)
> >> +			return ret;
> >> +
> >> +		reinit_completion(&ctlr->xfer_completion);
> >> +
> >> +		ret = ctlr->mem_ops->poll_status(mem, op, mask, match,
> >> +						 timeout_ms);
> >> +
> >> +		ms = wait_for_completion_timeout(&ctlr->xfer_completion,
> >> +						 msecs_to_jiffies(timeout_ms));  
> > 
> > Why do you need to wait here? I'd expect the poll_status to take care
> > of this wait.  
> 
> It was a request from Mark Brown [1]. The idea is to implement
> similar mechanism already used in SPI framework.

Well, you have to choose, either you pass a timeout to ->poll_status()
and let the driver wait for the status change (and return -ETIMEDOUT if
it didn't happen in time), or you do it here and the driver only has to
signal the core completion object. I think it's preferable to let the
driver handle the timeout though, because you don't know how the
status check will be implemented, and it's not like the
reinit_completion()+wait_for_completion_timeout() done here would
greatly simplify the drivers wait logic anyway.