linux-kernel - Re: [RFC PATCH 2/3] mtd: spi-nor: sfdp: fix spi_nor_read

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Message-ID: <20210316110400.kepjn6b654lhq4dy@ti.com>
Date:   Tue, 16 Mar 2021 16:34:02 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Michael Walle <michael@...le.cc>
CC:     <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>
Subject: Re: [RFC PATCH 2/3] mtd: spi-nor: sfdp: fix spi_nor_read_sfdp()

On 12/03/21 08:05PM, Michael Walle wrote:
> If spi_nor_read_sfdp() is used after probe, we have to set read_proto
> and the read dirmap.
> 
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
>  drivers/mtd/spi-nor/sfdp.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
> index b1814afefc33..47634ec9b899 100644
> --- a/drivers/mtd/spi-nor/sfdp.c
> +++ b/drivers/mtd/spi-nor/sfdp.c
> @@ -179,19 +179,27 @@ static int spi_nor_read_sfdp(struct spi_nor *nor, u32 addr,
>  			     size_t len, void *buf)
>  {
>  	u8 addr_width, read_opcode, read_dummy;
> +	struct spi_mem_dirmap_desc *rdesc;
> +	enum spi_nor_protocol read_proto;
>  	int ret;
>  
>  	read_opcode = nor->read_opcode;
> +	read_proto = nor->read_proto;
> +	rdesc = nor->dirmap.rdesc;
>  	addr_width = nor->addr_width;
>  	read_dummy = nor->read_dummy;
>  
>  	nor->read_opcode = SPINOR_OP_RDSFDP;
> +	nor->read_proto = SNOR_PROTO_1_1_1;
> +	nor->dirmap.rdesc = NULL;
>  	nor->addr_width = 3;
>  	nor->read_dummy = 8;

NACK. You can't assume the device is still in 1S-1S-1S mode after probe. 
For example, the s28hs512t flash is switched to 8D-8D-8D mode by the 
time the probe finishes so this would be an invalid command. Same for 
any flash that goes into a stateful mode.

And you can't even keep using nor->read_proto to read SFDP because the 
Read SFDP command might not be supported in all modes. xSPI spec 
(JESD251) says that the Read SFDP command is optional in 8D-8D-8D mode. 

I think the best approach for this would be to cache the entire SFDP 
table at parse time. This obviously comes with a memory overhead but I 
don't think it would be too big. For example, the sfdp table on 
s28hs512t is 491 bytes and it has 6 tables. Anyway, if the memory usage 
is too much of a problem we can put the feature behind a config.

>  
>  	ret = spi_nor_read_raw(nor, addr, len, buf);
>  
>  	nor->read_opcode = read_opcode;
> +	nor->read_proto = read_proto;
> +	nor->dirmap.rdesc = rdesc;
>  	nor->addr_width = addr_width;
>  	nor->read_dummy = read_dummy;
>  
> -- 
> 2.20.1
> 

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.