linux-kernel - Re: [PATCH 1/2] mtd: spi-nor: rework spi nor read and write.

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Message-ID: <CAOMqctRvoX9w9euyPqD_aBrz=d_pCC9AYKCg2HVrZ-tLOcAibQ@mail.gmail.com>
Date:	Wed, 29 Jul 2015 06:16:21 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Marek Vasut <marex@...x.de>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Han Xu <han.xu@...escale.com>,
	Rafał Miłecki <zajec5@...il.com>,
	Alison Chaiken <alison_chaiken@...tor.com>,
	Huang Shijie <b32955@...escale.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Gabor Juhos <juhosg@...nwrt.org>,
	Bean Huo 霍斌斌 (beanhuo) 
	<beanhuo@...ron.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mtd: spi-nor: rework spi nor read and write.

On 28 July 2015 at 20:15, Marek Vasut <marex@...x.de> wrote:
> On Tuesday, July 28, 2015 at 11:23:02 AM, Michal Suchanek wrote:
>> The spi_nor read and write functions pass thru the mtd retlen to the
>> chip-specific read and write function. This makes it difficult to check
>> for errors in read and write functions and these errors are not checked.
>> This leads to silent data corruption.
>>
>> This patch styles the chip-specific read and write function as unix
>> read(2) and write(2) and updates the retlen in the spi-nor generic driver.
>>
>> This also makes it possible to check for write errors.
>> When pl330 fails to transfer the flash data over SPI I get I/O error
>> instead of 4M of zeroes.
>>
>> I do not have sst and fsl hardware to test with.
>>
>> Signed-off-by: Michal Suchanek <hramrach@...il.com>
>> ---
>>  drivers/mtd/devices/m25p80.c      | 33 ++++++++++++++---------
>>  drivers/mtd/spi-nor/fsl-quadspi.c | 29 ++++++++++----------
>>  drivers/mtd/spi-nor/spi-nor.c     | 57
>> ++++++++++++++++++++++++++++----------- include/linux/mtd/spi-nor.h
>> |  8 +++---
>>  4 files changed, 81 insertions(+), 46 deletions(-)
>>
>> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
>> index d313f948b..d8f064b 100644
>> --- a/drivers/mtd/devices/m25p80.c
>> +++ b/drivers/mtd/devices/m25p80.c
>> @@ -75,14 +75,15 @@ static int m25p80_write_reg(struct spi_nor *nor, u8
>> opcode, u8 *buf, int len, return spi_write(spi, flash->command, len + 1);
>>  }
>>
>> -static void m25p80_write(struct spi_nor *nor, loff_t to, size_t len,
>> -                     size_t *retlen, const u_char *buf)
>> +static ssize_t m25p80_write(struct spi_nor *nor, loff_t to, size_t len,
>> +                         const u_char *buf)
>>  {
>>       struct m25p *flash = nor->priv;
>>       struct spi_device *spi = flash->spi;
>>       struct spi_transfer t[2] = {};
>>       struct spi_message m;
>>       int cmd_sz = m25p_cmdsz(nor);
>> +     ssize_t ret;
>>
>>       spi_message_init(&m);
>>
>> @@ -100,9 +101,14 @@ static void m25p80_write(struct spi_nor *nor, loff_t
>> to, size_t len, t[1].len = len;
>>       spi_message_add_tail(&t[1], &m);
>>
>> -     spi_sync(spi, &m);
>> +     ret = spi_sync(spi, &m);
>> +     if (ret)
>> +             return ret;
>>
>> -     *retlen += m.actual_length - cmd_sz;
>> +     ret = m.actual_length - cmd_sz;
>> +     if (ret < 0)
>> +             return -EIO;
>> +     return ret;
>
> I'd prefer to just add the return value and keep the retlen to keep error
> codes and transfer length separate.

I prefer to not pass around retlen because passing it around

 - causes code duplication
 - makes the code harder to understand

>
> btw. you change the transfer length from unsigned to signed type -- long
> transfer might get interpreted as an error.

Note that ssize_t is supposed to be enough for write(2) so when it
does not suffice you have a real system-wide problem.

That aside NOR flash sizes tend to be in the order of megabytes so
this concern is very theoretical.

Thanks

Michal
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