linux-kernel - Re: [PATCH v2 1/1] mtd: spi-nor: core: replace dummy buswidth from addr to data

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Message-Id: <D72GVBSZNP5J.1NMQYXQ4SZLNF@kernel.org>
Date: Wed, 15 Jan 2025 08:26:11 +0100
From: "Michael Walle" <mwalle@...nel.org>
To: "Pratyush Yadav" <pratyush@...nel.org>, "Miquel Raynal"
 <miquel.raynal@...tlin.com>
Cc: "Alexander Stein" <alexander.stein@...tq-group.com>,
 <tudor.ambarus@...aro.org>, <richard@....at>, <vigneshr@...com>,
 <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
 <alvinzhou@...c.com.tw>, <leoyu@...c.com.tw>, "Cheng Ming Lin"
 <chengminglin@...c.com.tw>, <stable@...r.kernel.org>, "Cheng Ming Lin"
 <linchengming884@...il.com>
Subject: Re: [PATCH v2 1/1] mtd: spi-nor: core: replace dummy buswidth from
 addr to data

Hi,

> >>>> --- a/drivers/mtd/spi-nor/core.c
> >>>> +++ b/drivers/mtd/spi-nor/core.c
> >>>> @@ -89,7 +89,7 @@ void spi_nor_spimem_setup_op(const struct spi_nor *nor,
> >>>>  		op->addr.buswidth = spi_nor_get_protocol_addr_nbits(proto);
> >>>>  
> >>>>  	if (op->dummy.nbytes)
> >>>> -		op->dummy.buswidth = spi_nor_get_protocol_addr_nbits(proto);
> >>>> +		op->dummy.buswidth = spi_nor_get_protocol_data_nbits(proto);
> >
> > Facing recently a similar issue myself in the SPI NAND world, I believe
> > we should get rid of the notion of bits when it comes to the dummy
> > phase. I would appreciate a clarification like "dummy.cycles" which
> > would typically not require any bus width implications.
>
> I agree. All peripheral drivers convert cycles to bytes, and controller
> drivers convert them back to cycles. This whole thing should be avoided,
> especially since it contains some traps with division truncation.

Here is the relevant discussion:
https://lore.kernel.org/linux-mtd/f647e713a65f5d3f0f2e3af95c4d0a89@walle.cc/

TLDR: yes, please use the notion of (clock) cycles. But there are
some problems to solve first.

> >> Since we are quite late in the cycle, and that changing
> >> spi_mem_check_buswidth() might cause all sorts of breakages, I think the
> >> best idea currently would be to revert this patch, and resend it with
> >> the other changes later.
> >>
> >> Tudor, Michael, Miquel, what do you think about this? We are at rc7 but
> >> I think we should send out a fixes PR with a revert. If you agree, I
> >> will send out a patch and a PR.
> >
> > Either way I am fine. the -rc cycles are also available for us to
> > settle. But it's true we can bikeshed a little bit, so feel free to
> > revert this patch before sending the MR.
>
> To be clear, since the patch was added in v6.13-rc1 I want to revert it
> via a fixes pull request to Linus before he releases v6.13 this week. I
> want to fix it in v6.13, not in v6.14.

Since it's clearly a regression, I'd revert it.

-michael

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