linux-kernel - Re: [RFC PATCH 1/3] mtd: spi-nor: sfdp: remember sfdp

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Message-ID: <3deb91e2c9fc3f62ae6976cecae37bf3@walle.cc>
Date:   Tue, 16 Mar 2021 12:22:25 +0100
From:   Michael Walle <michael@...le.cc>
To:     Pratyush Yadav <p.yadav@...com>
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 1/3] mtd: spi-nor: sfdp: remember sfdp_size

Am 2021-03-16 12:06, schrieb Pratyush Yadav:
> On 16/03/21 12:01PM, Michael Walle wrote:
>> Hi Pratyush,
>> 
>> Am 2021-03-16 11:42, schrieb Pratyush Yadav:
>> > On 12/03/21 08:05PM, Michael Walle wrote:
>> > > Save the sftp_size in the spi_nor struct so we can use it to dump the
>> > > SFDP table without parsing the headers again.
>> > >
>> > > Signed-off-by: Michael Walle <michael@...le.cc>
>> > > ---
>> > >  drivers/mtd/spi-nor/sfdp.c  | 12 ++++++++++++
>> > >  include/linux/mtd/spi-nor.h |  1 +
>> > >  2 files changed, 13 insertions(+)
>> > >
>> > > diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
>> > > index 25142ec4737b..b1814afefc33 100644
>> > > --- a/drivers/mtd/spi-nor/sfdp.c
>> > > +++ b/drivers/mtd/spi-nor/sfdp.c
>> > > @@ -16,6 +16,7 @@
>> > >  	(((p)->parameter_table_pointer[2] << 16) | \
>> > >  	 ((p)->parameter_table_pointer[1] <<  8) | \
>> > >  	 ((p)->parameter_table_pointer[0] <<  0))
>> > > +#define SFDP_PARAM_HEADER_PARAM_LEN(p) ((p)->length * 4)
>> > >
>> > >  #define SFDP_BFPT_ID		0xff00	/* Basic Flash Parameter Table */
>> > >  #define SFDP_SECTOR_MAP_ID	0xff81	/* Sector Map Table */
>> > > @@ -1263,6 +1264,7 @@ int spi_nor_parse_sfdp(struct spi_nor *nor,
>> > >  	struct sfdp_parameter_header *param_headers = NULL;
>> > >  	struct sfdp_header header;
>> > >  	struct device *dev = nor->dev;
>> > > +	size_t param_max_offset;
>> > >  	size_t psize;
>> > >  	int i, err;
>> > >
>> > > @@ -1285,6 +1287,9 @@ int spi_nor_parse_sfdp(struct spi_nor *nor,
>> > >  	    bfpt_header->major != SFDP_JESD216_MAJOR)
>> > >  		return -EINVAL;
>> > >
>> > > +	nor->sfdp_size = SFDP_PARAM_HEADER_PTP(bfpt_header) +
>> > > +			 SFDP_PARAM_HEADER_PARAM_LEN(bfpt_header);
>> > > +
>> > >  	/*
>> > >  	 * Allocate memory then read all parameter headers with a single
>> > >  	 * Read SFDP command. These parameter headers will actually be
>> > > parsed
>> > > @@ -1311,6 +1316,13 @@ int spi_nor_parse_sfdp(struct spi_nor *nor,
>> > >  		}
>> > >  	}
>> > >
>> > > +	for (i = 0; i < header.nph; i++) {
>> > > +		param_header = &param_headers[i];
>> > > +		param_max_offset = SFDP_PARAM_HEADER_PTP(param_header) +
>> > > +				   SFDP_PARAM_HEADER_PARAM_LEN(param_header);
>> > > +		nor->sfdp_size = max(nor->sfdp_size, param_max_offset);
>> > > +	}
>> > > +
>> >
>> > I don't see any mention in the SFDP spec (JESD216D-01) that parameter
>> > tables have to be contiguous.
>> 
>> ch. 6.1, fig.10 looks like all the headers come after the initial SFDP
>> header. If that wasn't the case, how would you find the headers then?
>> 
>> Also ch. 6.3
>> """All subsequent parameter headers need to be contiguous and may be
>> specified..."""
>> 
>> > In fact, it says that "Parameter tables
>> > may be located anywhere in the SFDP space. They do not need to
>> > immediately follow the parameter headers".
>> 
>> The tables itself, yes, but not the headers for the tables.
> 
> Yes, I was talking about the tables and not the headers. There might be
> holes in the SFDP space but I don't think it would be a problem.

Ah, ok. Well basically I'm assuming that the holes will returning some
sane values. Or you could dump the space together with a mask. But that
is overkill ;)

-michael