[OpenWrt-Devel] [PATCH] ramips: Increase GB-PC2 SPI speed to 50MHz

[Rosen Penev]

On Sun, Feb 10, 2019 at 8:59 PM Chuanhong Guo <gch981213 at gmail.com> wrote:
>
> Hi!
> On Mon, Feb 11, 2019 at 7:49 AM Rosen Penev <rosenp at gmail.com> wrote:
> > [...]
> > On the PC1, I can go even higher with the SPI frequency to get better
> > performance. However, the later versions of the PC1 switched flash
> > chips to Spansion to avoid a restart bug. Those are documented as
> > accepting 50MHz for read requests.
>
> FYI: I haven't check the Spansion datasheet, but when Winbond
> datasheets say read instruction accepts SPI clock up to 50MHz it
> refers to the normal read instruction (0x03) and for higher clock you
> should switch to fast read instruction (0x0B) which can be done by
> adding m25p,fast-read to dts. I guess the situation with Spansion
> datasheets are the same.
Wow, thanks for that fast read hint. According to a datasheet I found
online, it accepts 50MHz for normal reads and 133MHz for fast reads. I
then increased the speed to 80MHz and ran again:

time dd if=/dev/mtdblock3 of=/dev/null = 6.15s
44.854483 seconds for jffs2 to complete building.

I then increased to 104MHz
time dd if=/dev/mtdblock3 of=/dev/null = 6.23s
44.312618 seconds for jffs2 to complete building

108MHz:
time dd if=/dev/mtdblock3 of=/dev/null = 6.28s
44.501574 seconds for jffs2 to complete building

I went back down to 50MHz just to make sure.
time dd if=/dev/mtdblock3 of=/dev/null = 8.68s
46.344117 seconds for jffs2 to complete building

then to 60MHz:
time dd if=/dev/mtdblock3 of=/dev/null = 7.37s
46.172334 seconds for jffs2 to complete building

and finally 66MHz:
time dd if=/dev/mtdblock3 of=/dev/null
45.501151 seconds for jffs2 to complete building

133MHz and 125MHz did not work. The datasheet mentions 66MHz for
mismatching core and I/O voltage and 133MHz for matching. 80MHz is
still faster though...

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