[PATCH/RFC -nxt] mtd_blkdevs: Set GENHD_FL_NO_PART

[PATCH/RFC -nxt] mtd_blkdevs: Set GENHD_FL_NO_PART

[Geert Uytterhoeven]

When DT declares the partitions of an spi-nor device using
"fixed-partitions", the individual mtdblockN partitions are now scanned
for partitition tables, which should not happen.

Fix this by setting the GENHD_FL_NO_PART flag in the MTD block layer
interface.

Fixes: 1ebe2e5f9d68e94c ("block: remove GENHD_FL_EXT_DEVT")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Seen with e.g. arch/arm/boot/dts/r8a7791-koelsch.dts.
I only noticed because I have debug code to measure QSPI performance,
which informed me about 8 x 512 bytes being read from each partition
detected.

RFC as I'm not sure this is correct in all cases.
I did verify that in the absence of "fixed-partitions", the spi-nor
device is not scanned for partitions before and after commit
1ebe2e5f9d68e94c.
---
 drivers/mtd/mtd_blkdevs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 113f86df76038575..95c84faa794d22c6 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -345,6 +345,7 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 	gd->first_minor = (new->devnum) << tr->part_bits;
 	gd->minors = 1 << tr->part_bits;
 	gd->fops = &mtd_block_ops;
+	gd->flags |= GENHD_FL_NO_PART;
 
 	if (tr->part_bits)
 		if (new->devnum < 26)
-- 
2.25.1

Re: [PATCH/RFC -nxt] mtd_blkdevs: Set GENHD_FL_NO_PART

[Christoph Hellwig]

On Tue, Nov 30, 2021 at 05:23:46PM +0100, Geert Uytterhoeven wrote:
> When DT declares the partitions of an spi-nor device using
> "fixed-partitions", the individual mtdblockN partitions are now scanned
> for partitition tables, which should not happen.
> 
> Fix this by setting the GENHD_FL_NO_PART flag in the MTD block layer
> interface.
> 
> Fixes: 1ebe2e5f9d68e94c ("block: remove GENHD_FL_EXT_DEVT")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> Seen with e.g. arch/arm/boot/dts/r8a7791-koelsch.dts.
> I only noticed because I have debug code to measure QSPI performance,
> which informed me about 8 x 512 bytes being read from each partition
> detected.
> 
> RFC as I'm not sure this is correct in all cases.
> I did verify that in the absence of "fixed-partitions", the spi-nor
> device is not scanned for partitions before and after commit
> 1ebe2e5f9d68e94c.

As far as I can tell mtd fixed partitions have nothing to do with
the block layer concept of partitions.  What kind of behavior change
did you see?

Re: [PATCH/RFC -nxt] mtd_blkdevs: Set GENHD_FL_NO_PART

[Geert Uytterhoeven]

Hi Christoph,

On Wed, Dec 1, 2021 at 8:23 AM Christoph Hellwig <hch@lst.de> wrote:
> On Tue, Nov 30, 2021 at 05:23:46PM +0100, Geert Uytterhoeven wrote:
> > When DT declares the partitions of an spi-nor device using
> > "fixed-partitions", the individual mtdblockN partitions are now scanned
> > for partitition tables, which should not happen.
> >
> > Fix this by setting the GENHD_FL_NO_PART flag in the MTD block layer
> > interface.
> >
> > Fixes: 1ebe2e5f9d68e94c ("block: remove GENHD_FL_EXT_DEVT")
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > ---
> > Seen with e.g. arch/arm/boot/dts/r8a7791-koelsch.dts.
> > I only noticed because I have debug code to measure QSPI performance,
> > which informed me about 8 x 512 bytes being read from each partition
> > detected.
> >
> > RFC as I'm not sure this is correct in all cases.
> > I did verify that in the absence of "fixed-partitions", the spi-nor
> > device is not scanned for partitions before and after commit
> > 1ebe2e5f9d68e94c.
>
> As far as I can tell mtd fixed partitions have nothing to do with
> the block layer concept of partitions.  What kind of behavior change
> did you see?

After the aforementioned commit, 8 x 512 bytes are being read from
the start of each partition described by "fixed-partitions".
Dmesg difference with debug print added to spi_nor_spimem_read_data():

  renesas_spi e6b10000.spi: registered master spi0
  spi spi0.0: setup mode 3, 8 bits/w, 30000000 Hz max --> 0
  spi-nor spi0.0: s25fl512s (65536 Kbytes)
  3 fixed-partitions partitions found on MTD device spi0.0
  Creating 3 MTD partitions on "spi0.0":
  0x000000000000-0x000000080000 : "loader"
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 0 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 512 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 1024 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 1536 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 2048 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 2560 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 3072 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 3584 len 512
  0x000000080000-0x000000600000 : "user"
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 524288 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 524800 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 525312 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 525824 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 526336 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 526848 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 527360 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 527872 len 512
  0x000000600000-0x000004000000 : "flash"
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6291456 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6291968 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6292480 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6292992 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6293504 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6294016 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6294528 len 512
+ spi-nor spi0.0: spi_nor_spimem_read_data: from 6295040 len 512
  renesas_spi e6b10000.spi: registered child spi0.0
  renesas_spi e6b10000.spi: probed

Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH/RFC -nxt] mtd_blkdevs: Set GENHD_FL_NO_PART

[Christoph Hellwig]

I think we need the patch below to restore the old behavior where a
partitions scan happens only for those sub-drivers that do report a
partition shift.

MTD maintainers: is this intentional that raw mtdblock does not support
partitions, but the various "FTL" modules do?

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 113f86df76038..57a22d2ebaeca 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -345,6 +345,8 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 	gd->first_minor = (new->devnum) << tr->part_bits;
 	gd->minors = 1 << tr->part_bits;
 	gd->fops = &mtd_block_ops;
+	if (!tr->part_bits)
+		gd->flags |= GENHD_FL_NO_PART;
 
 	if (tr->part_bits)
 		if (new->devnum < 26)

Re: [PATCH/RFC -nxt] mtd_blkdevs: Set GENHD_FL_NO_PART

[Geert Uytterhoeven]

Hi Christoph,

On Fri, Dec 3, 2021 at 7:57 AM Christoph Hellwig <hch@lst.de> wrote:
> I think we need the patch below to restore the old behavior where a
> partitions scan happens only for those sub-drivers that do report a
> partition shift.

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

> MTD maintainers: is this intentional that raw mtdblock does not support
> partitions, but the various "FTL" modules do?
>
> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> index 113f86df76038..57a22d2ebaeca 100644
> --- a/drivers/mtd/mtd_blkdevs.c
> +++ b/drivers/mtd/mtd_blkdevs.c
> @@ -345,6 +345,8 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
>         gd->first_minor = (new->devnum) << tr->part_bits;
>         gd->minors = 1 << tr->part_bits;
>         gd->fops = &mtd_block_ops;
> +       if (!tr->part_bits)
> +               gd->flags |= GENHD_FL_NO_PART;

Move this into the "else" branch of the test below?

>         if (tr->part_bits)
>                 if (new->devnum < 26)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds