linux-kernel - Re: [PATCH v2] mtd: spi-nor: Return error when nor->addr

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Message-ID: <823dcd3f-8b9f-15c5-a072-06625120766e@ti.com>
Date:   Tue, 19 Mar 2019 10:52:15 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Liu Xiang <liu.xiang6@....com.cn>, <bbrezillon@...nel.org>
CC:     <richard@....at>, <linux-kernel@...r.kernel.org>,
        <marek.vasut@...il.com>, <linux-mtd@...ts.infradead.org>,
        <liuxiang_1999@....com>, <computersforpeace@...il.com>,
        <dwmw2@...radead.org>
Subject: Re: [PATCH v2] mtd: spi-nor: Return error when nor->addr_width does
 not match the device size

Hi,

On 13/03/19 7:15 PM, Liu Xiang wrote:
> In some is25lp256, the DWORD1 of JEDEC Basic Flash Parameter Header
> is 0xfff920e5. So the DWORD1[18:17] Address Bytes bits are 0b00,
> means that 3-Byte only addressing. But the device size is larger
> than 16MB, nor->addr_width must be 4 to access the whole address.
> An error should be returned when nor->addr_width does not match
> the device size in spi_nor_parse_bfpt(). Then it can go back to
> use spi_nor_ids[] for setting the right addr_width.
> 
> Suggested-by: Boris Brezillon <boris.brezillon@...tlin.com>
> Signed-off-by: Liu Xiang <liu.xiang6@....com.cn>
> ---
>  drivers/mtd/spi-nor/spi-nor.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 6e13bbd..63933c7 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -2811,6 +2811,14 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
>  	}
>  	params->size >>= 3; /* Convert to bytes. */
>  
> +	/*
> +	 * If the device exceeds 16MiB, addr_width must be 4.
> +	 * addr_width == 3 means the Address Bytes we are
> +	 * reading from BFPT is wrong.
> +	 */

JESD216 standard does not mandate flash devices >16MiB to always support
4 byte addressing opcode. So, its okay for flash vendor to support
>16MiB flash with 3 byte addressing and Bank/extended address register.

> +	if (params->size > 0x1000000 && nor->addr_width == 3)
> +		return -EINVAL;
> +

Assuming only DWORD1[18:17] bits are wrong, then returning from here
would mean we miss parsing Sector Erase settings, Quad Enable
Requirements etc from BFPT which is kind of bad.
I suggest to move the fix to[1], addr_width indicated in flash_info
struct of the device can take precedence over SFDP.

[1]https://elixir.bootlin.com/linux/latest/source/drivers/mtd/spi-nor/spi-nor.c#L4106


>  	/* Fast Read settings. */
>  	for (i = 0; i < ARRAY_SIZE(sfdp_bfpt_reads); i++) {
>  		const struct sfdp_bfpt_read *rd = &sfdp_bfpt_reads[i];
> 

-- 
Regards
Vignesh