Re: [PATCH v2 1/2] mtd: spi-nor: macronix: add support for Macronix octaflash

[Pratyush Yadav <p.yadav@xxxxxx>]

On 23/02/21 01:36PM, Mark Brown wrote:
> On Tue, Feb 23, 2021 at 02:13:44PM +0100, Miquel Raynal wrote:
> > Pratyush Yadav <p.yadav@xxxxxx> wrote on Fri, 5 Feb 2021 19:04:04 +0530:
> 
> > > [0] Since SPI NOR has no way of knowing what speed the controller is 
> > > running at, assume the fastest speed the flash can run at.
> 
> > Ok, I am not entirely clear about what is available/not available from
> > the SPI core.
> 
> > If this is true then I guess we can't do better with the current code
> > base and this can be improved in the future if needed. So I'm fine with
> > the current implementation.
> 
> For normal SPI operations you can set the speed (really, top speed) on a
> per transfer basis.

To select the optimal number of dummy cycles we need to know what speed 
the controller is running at, not the other way around. The flash would 
always set the top speed to its maximum (say 200 MHz). But if the 
controller is only capable of running at 50 MHz, you will end up wasting 
dummy cycles. I don't see any API to communicate speed from controller 
to flash.

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.