[PATCH v7 2/3] mtd: rawnand: Enable monolithic read when reading subpages

[Keguang Zhang]

Sorry!
I admit this is taking a shortcut.
Will drop this patch and implement subpage read instead.
Thanks!

On Mon, May 20, 2024 at 11:33 PM Miquel Raynal

<miquel.raynal at bootlin.com> wrote:
>
> Hi Keguang,
>
> keguang.zhang at gmail.com wrote on Mon, 20 May 2024 18:42:30 +0800:
>
> > On Mon, May 6, 2024 at 3:17 PM Miquel Raynal <miquel.raynal at bootlin.com> wrote:
> > >
> > > Hi,
> > >
> > > devnull+keguang.zhang.gmail.com at kernel.org wrote on Tue, 30 Apr 2024
> > > 19:11:11 +0800:
> > >
> > > > From: Keguang Zhang <keguang.zhang at gmail.com>
> > > >
> > > > nand_read_subpage() reads data and ECC data by two separate
> > > > operations.
> > > > This patch allows the NAND controllers who support
> > > > monolithic page read to do subpage read by a single operation,
> > > > which is more effective than nand_read_subpage().
> > >
> > > I am a bit puzzled by this change. Usually nand_read_subpage is used
> > > for optimizations (when less data than a full page must be retrieved).
> > > I know it may be used in other cases (because it's easier for the core
> > > in order to support a wide range of controllers). Can you please show a
> > > speed test showing the results before I consider merging this patch?
> > >
> > With this patch:
> > # flash_speed -c 128 -d /dev/mtd1
> > scanning for bad eraseblocks
> > scanned 128 eraseblocks, 0 are bad
> > testing eraseblock write speed
> > eraseblock write speed is 2112 KiB/s
> > testing eraseblock read speed
> > eraseblock read speed is 3454 KiB/s
> > testing page write speed
> > page write speed is 1915 KiB/s
> > testing page read speed
> > page read speed is 2999 KiB/s
> > testing 2 page write speed
> > 2 page write speed is 2000 KiB/s
> > testing 2 page read speed
> > 2 page read speed is 3207 KiB/s
> > Testing erase speed
> > erase speed is 72495 KiB/s
> > Testing 2x multi-block erase speed
> > 2x multi-block erase speed is 74135 KiB/s
> > Testing 4x multi-block erase speed
> > 4x multi-block erase speed is 74812 KiB/s
> > Testing 8x multi-block erase speed
> > 8x multi-block erase speed is 75502 KiB/s
> > Testing 16x multi-block erase speed
> > 16x multi-block erase speed is 75851 KiB/s
> > Testing 32x multi-block erase speed
> > 32x multi-block erase speed is 75851 KiB/s
> > Testing 64x multi-block erase speed
> > 64x multi-block erase speed is 76204 KiB/s
> > finished
> >
> > Without this patch:
> > # flash_speed -c 128 -d /dev/mtd1
> > scanning for bad eraseblocks
> > scanned 128 eraseblocks, 0 are bad
> > testing eraseblock write speed
> > eraseblock write speed is 2074 KiB/s
> > testing eraseblock read speed
> > eraseblock read speed is 2895 KiB/s
> > testing page write speed
> > page write speed is 998 KiB/s
> > testing page read speed
> > page read speed is 1499 KiB/s
> > testing 2 page write speed
> > 2 page write speed is 1002 KiB/s
> > testing 2 page read speed
> > 2 page read speed is 1554 KiB/s
> > Testing erase speed
> > erase speed is 76560 KiB/s
> > Testing 2x multi-block erase speed
> > 2x multi-block erase speed is 74019 KiB/s
> > Testing 4x multi-block erase speed
> > 4x multi-block erase speed is 74769 KiB/s
> > Testing 8x multi-block erase speed
> > 8x multi-block erase speed is 75149 KiB/s
> > Testing 16x multi-block erase speed
> > 16x multi-block erase speed is 75921 KiB/s
> > Testing 32x multi-block erase speed
> > 32x multi-block erase speed is 75921 KiB/s
> > Testing 64x multi-block erase speed
> > 64x multi-block erase speed is 75921 KiB/s
> > finished
> >
> > The throughput of the former is twice that of the latter.
>
> And what is your NAND controller driver?
>
> subpage reads are used when you only want to read a subset of a NAND
> page.
>
> Otherwise the core may use the RNDOUT command to change the pointer in
> the chip's SRAM to read from a different location, but I don't see what
> is impacting so much, unless if the driver implementation is really
> sub-optimized.
>
> Thanks,
> Miquèl



--
Best regards,

Keguang Zhang