Re: [PATCH] spi: spi-imx: Revert "spi: spi-imx: add PIO polling support"

[Fabio Estevam <festevam@xxxxxxxxx>]

Hi David,

On Fri, Nov 11, 2022 at 6:50 AM David Jander <david@xxxxxxxxxxx> wrote:

> The effect of this patch is that it will cause short SPI transfers to have a
> lot less latency than without this patch, so could it be that we are looking
> at a timing related bug in the MTD driver, or some other timing issue?
> Your SPI clock is 80MHz, but the datasheet of the MACRONIX MX25R1635F
> specifies a maximum clock of 33MHz. Is your NOR flash chip capable of this
> clock-rate?

Thanks for your suggestions.

I have tried passing spi-max-frequency = <33000000>, and I don't see
the failure anymore.

Looking at the MX25R1635F datasheet the maximum SPI frequency is:

80MHz: when L/H bit is 1 - High Performance mode.
33MHz: when L/H bit is 0 - Ultra Low Power mode.

"L/H switch bit The Low Power / High Performance bit is a volatile bit.
User can change the value of L/H switch bit to keep Ultra Low Power
mode or High Performance mode.
Please check Ordering Information for the L/H Switch default support"

Frieder,

Could it be that the MX25R1635F part that on the Kontron imx8mm SoM has the
Ultra Low Power Mode selected by default?

If that's the case, I can send a patch that changes the
spi-max-frequency from 80MHz to 33MHz.

Thanks