linux-kernel - Re: [PATCH/RFC] mtd: spi-nor: honour max_message

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Date:   Wed, 9 May 2018 16:02:40 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     NeilBrown <neil@...wn.name>, Marek Vasut <marek.vasut@...il.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] mtd: spi-nor: honour max_message_size for spi-nor
 writes.

On Fri, 27 Apr 2018 16:18:05 +1000
NeilBrown <neil@...wn.name> wrote:

> Hi,
>  I've labeled this an RFC because I'm really not sure about removing the
>  error path from spi_nor_write() -- maybe that really matters.  But on
>  my hardware, performing multiple small spi writes to the flash seems
>  to work.
> 
>  The spi driver is drivers/staging/mt7621-spi.  Possibly this needs to
>  use DMA instead of a FIFO (assuming the hardware can) - or maybe
>  drivers/spi/spi-mt65xx.c can be made to work on this hardware, though
>  that is for an ARM SOC and mt7621 is a MIPS SOC.
> 
>  I note that openwrt has similar patches:
>   target/linux/generic/pending-4.14/450-mtd-spi-nor-allow-NOR-driver-to-write-fewer-bytes-th.patch
> 
>  They also change the spi driver to do a short write, rather
>  than change m25p80 to request a short write.
> 
>  Is there something horribly wrong with this?

Marek, any opinion on this patch?

> 
> Thanks,
> NeilBrown
> 
> -----------------------8<------------------------
> 
> m25p80 honours max_message_size and max_transfer_size
> for reads, but not for writes.
> I have a driver that has a max message size of 36 bytes
> (command, address, 32 bytes data, all places in a FIFO
> in the controller).
> This requires m25p80_write() to honour the size limits.
> For that to work, spi-nor needs to quietly accept partial
> writes.
> 
> With this, I can successfully re-flash my device.
> 
> Signed-off-by: NeilBrown <neil@...wn.name>
> ---
>  drivers/mtd/devices/m25p80.c  | 3 ++-
>  drivers/mtd/spi-nor/spi-nor.c | 7 -------
>  2 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index a4e18f6aaa33..7ded13507604 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -117,7 +117,8 @@ static ssize_t m25p80_write(struct spi_nor *nor, loff_t to, size_t len,
>  
>  	t[data_idx].tx_buf = buf;
>  	t[data_idx].tx_nbits = data_nbits;
> -	t[data_idx].len = len;
> +	t[data_idx].len = min3(len, spi_max_transfer_size(spi),
> +			       spi_max_message_size(spi) - cmd_sz);
>  	spi_message_add_tail(&t[data_idx], &m);
>  
>  	ret = spi_sync(spi, &m);
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 42ae9a1529bb..cfa15f2801ad 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -1445,13 +1445,6 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t to, size_t len,
>  			goto write_err;
>  		*retlen += written;
>  		i += written;
> -		if (written != page_remain) {
> -			dev_err(nor->dev,
> -				"While writing %zu bytes written %zd bytes\n",
> -				page_remain, written);
> -			ret = -EIO;
> -			goto write_err;
> -		}
>  	}
>  
>  write_err: