From: Michael Walle <michael@walle.cc>
To: Pratyush Yadav <p.yadav@ti.com>
Cc: linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
Tudor Ambarus <tudor.ambarus@microchip.com>,
Miquel Raynal <miquel.raynal@bootlin.com>,
Richard Weinberger <richard@nod.at>,
Vignesh Raghavendra <vigneshr@ti.com>
Subject: Re: [PATCH 1/2] mtd: spi-nor: sfdp: save a copy of the SFDP data
Date: Mon, 22 Mar 2021 23:31:39 +0100 [thread overview]
Message-ID: <7e00a5fc05a186d5b34916e5a9f45a48@walle.cc> (raw)
In-Reply-To: <20210322184214.ernzjfwfle6dfhpv@ti.com>
Am 2021-03-22 19:42, schrieb Pratyush Yadav:
> On 22/03/21 04:32PM, Michael Walle wrote:
>> Am 2021-03-22 15:21, schrieb Pratyush Yadav:
>> > On 18/03/21 10:24AM, Michael Walle wrote:
>> > > +
>> > > + sfdp->num_dwords = DIV_ROUND_UP(sfdp_size, sizeof(*sfdp->dwords));
>> >
>> > The SFDP spec says that Parameter Table Pointer should be DWORD aligned
>> > and Parameter Table length is specified in number of DWORDs. So,
>> > sfdp_size should always be a multiple of 4. Any SFDP table where this is
>> > not true is an invalid one.
>> >
>> > Also, the spec says "Device behavior when the Read SFDP command crosses
>> > the SFDP structure boundary is not defined".
>> >
>> > So I think this should be a check for alignment instead of a round-up.
>>
>> Well, that woundn't help for debugging. I.e. you also want the SFDP
>> data
>> in cases like this. IMHO we should try hard enough to actually get a
>> reasonable dump.
>>
>> OTOH we also rely on the header and the pointers in the header. Any
>> other ideas, but just to chicken out?
>
> Honestly, I don't think reading past the SFDP boundary would be too
> bad.
> It probably will just be some garbage data. But if you want to avoid
> that, you can always round down instead of up.
Like I said, while the storage will be rounded up to a multiple of
DWORDs, only sfdp_size is transferred. Thus it case a pointer is not
DWORD aligned, we end up with zeros at the end.
I'll add a comment.
> This way you will only
> miss the last DWORD at most. In either case, a warning should be
> printed
> so this problem can be brought to the user's attention.
I was about to add a warning/debug message. But its the wrong place.
It should really be checked in the for loop which iterates over the
headers before parsing them. You could check sfdp_size but then two
unaligned param pointers might cancel each other out.
This can be a seperate patch, besides adding a warning, should there
be any other things to do, e.g. stop parsing and error out?
..
>> > > + goto exit;
>> > > + }
>> > > +
>> > > + err = spi_nor_read_sfdp_dma_unsafe(nor, 0, sfdp_size, sfdp->dwords);
Btw, this can be spi_nor_read_sfdp(). But I'm not sure, what this
whole dma capable buffer should be. Is kmalloc(GFP_KERNEL)
considered DMA safe?
The buffer ends in spi_nor_read_data(), which is also called from
mtdcore:
spi_nor_read_sfdp()
spi_nor_read_raw()
spi_nor_read_data()
mtd_read()
mtd_read_oob()
mtd_read_oob_std()
spi_nor_read()
spi_nor_read_data()
Is the buffer passed from mtd_read() also DMA-safe? Doesn't the SPI
drivers allocate DMA safe buffers if they need them?
-michael
next prev parent reply other threads:[~2021-03-22 22:32 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 9:24 [PATCH 0/2] mtd: spi-nor: support dumping sfdp tables Michael Walle
2021-03-18 9:24 ` [PATCH 1/2] mtd: spi-nor: sfdp: save a copy of the SFDP data Michael Walle
2021-03-22 14:21 ` Pratyush Yadav
2021-03-22 15:32 ` Michael Walle
2021-03-22 15:48 ` Michael Walle
2021-03-22 18:42 ` Pratyush Yadav
2021-03-22 22:31 ` Michael Walle [this message]
2021-03-23 9:37 ` Pratyush Yadav
2021-04-05 13:11 ` Tudor.Ambarus
2021-04-05 15:07 ` Michael Walle
2021-04-05 15:42 ` Tudor.Ambarus
2021-04-05 16:03 ` Michael Walle
2021-03-18 9:24 ` [PATCH 2/2] mtd: spi-nor: add initial sysfs support Michael Walle
2021-03-20 4:16 ` Yicong Yang
2021-03-20 19:17 ` Michael Walle
2021-03-22 14:43 ` Pratyush Yadav
2021-03-22 14:57 ` Michael Walle
2021-04-06 7:56 ` Vignesh Raghavendra
2021-04-06 8:47 ` Michael Walle
2021-04-06 11:43 ` Vignesh Raghavendra
2021-04-29 15:37 ` Alexander Williams
2021-04-29 15:46 ` Michael Walle
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