Re: [RFC PATCH v2 00/12] spi: cadence-quadspi: add PHY tuning support

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Santhosh,

> I am surprised by these numbers, I would expect these to get higher for
> SPI NANDs. I will test the series and report my observations, especially
> since there is also ODDR SPI NAND support now (in nand/next, should be
> part of my upcoming merge request to Linus for 6.19+1);

I just tested the series, here are some numbers I grabbed on TI AM62A7
LP SK with a Winbond W35N02 SPI NAND chip (so in the end very close to
your report):

 +-----------------+-----------+------------+
 | SPI NAND        | no tuning | PHY tuning |
 | Unit: MiB/s     |   25MHz   |   166MHz   |
 |-----------------+-----------+------------|           
 | Octal SDR read  |   13.8    |    34.2    |
 |           write |    7.2    |    10.2    |
 |-----------------+-----------+------------|
 | Octal DTR read  |   21.2    |     N/A    |
 |           write |    9.0    |     N/A    |
 +-----------------+-----------+------------+

Please mind I used MiB/s and not MB/s (so kiB / 1024), I don't know
which one you used for measuring, as you marked MB, whereas the most
common unit seems to be MiB.

However PHY tuning failed in Octal DTR mode (your series applied on top
of nand/next) with the following logs, can you have a look?

[    2.261647] spi-nand spi0.0: Winbond SPI NAND was found.
[    2.266956] spi-nand spi0.0: 128 MiB, block size: 256 KiB, page size: 4096, OOB size: 128
[    2.285257] cadence-qspi fc40000.spi: PHY tuning failed: -2
[    2.290835] spi-nand spi0.0: Failed to execute PHY tuning: -2

The fallback worked well though, the memory was still usable like
before, which is a very good point.

Thanks,
Miquèl