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

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Date:   Mon, 26 Apr 2021 23:09:36 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Mark Brown <broonie@...nel.org>
CC:     <patrice.chotard@...s.st.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <boris.brezillon@...labora.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 1/3] spi: spi-mem: add automatic poll status functions

On 26/04/21 05:51PM, Mark Brown wrote:
> On Mon, Apr 26, 2021 at 09:56:12PM +0530, Pratyush Yadav wrote:
> > On 26/04/21 04:39PM, patrice.chotard@...s.st.com wrote:
> 
> > > + * spi_mem_poll_status() - Poll memory device status
> > > + * @mem: SPI memory device
> > > + * @op: the memory operation to execute
> > > + * @mask: status bitmask to ckeck
> > > + * @match: status expected value
> 
> > Technically, (status & mask) expected value. Dunno if that is obvious 
> > enough to not spell out explicitly.
> 
> Is it possible there's some situation where you're waiting for some bits
> to clear as well?

Yes. In fact, that is the more common situation. Both SPI NOR 
(spi_nor_sr_ready()) and SPI NAND (spinand_wait()) need to wait for the 
"busy" bit to be cleared.

AFAICT this API is supposed to check for (status & mask) == (match & 
mask) so it should be able to handle both polarities for the bits being 
polled.

> 
> > > +		ret = ctlr->mem_ops->poll_status(mem, op, mask, match, timeout);
> 
> I'm not sure I like this name since it makes me think the driver is
> going to poll when really it's offloaded to the hardware, but I can't
> think of any better ideas either and it *is* what the hardware is going
> to be doing so meh.
> 
> > I wonder if it is better to let spi-mem core take care of the timeout 
> > part. On one hand it reduces code duplication on the driver side a 
> > little bit. Plus it makes sure drivers don't mess anything up with bad 
> > (or no) handling of the timeout. But on the other hand the interface 
> > becomes a bit awkward since you'd have to pass a struct completion 
> > around, and it isn't something particularly hard to get right either. 
> > What do you think?
> 
> We already have the core handling other timeouts.  We don't pass around
> completions but rather have an API function that the driver has to call
> when the operation completes, a similar pattern might work here.  Part
> of the thing with those APIs which I'm missing here is that this will
> just return -EOPNOTSUPP if the driver can't do the delay in hardware, I
> think it would be cleaner if this API were similar and the core dealt
> with doing the delay/poll on the CPU.  That way the users don't need to
> repeat the handling for the offload/non-offload cases.

Makes sense to me.

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.