Re: [PATCH 1/2] mtd: spi-nor: When a flash memory is missing do not report an error

[Michael Walle]

Am 2022-07-14 22:55, schrieb Michal Suchánek:
> On Thu, Jul 14, 2022 at 09:41:48PM +0200, Michael Walle wrote:
> > Hi,
> >
> > Am 2022-07-14 21:19, schrieb Michal Suchanek:
> > > It is normal that devices are designed with multiple types of storage,
> > > and only some types of storage are present.
> > >
> > > The kernel can handle this situation gracefully for many types of
> > > storage devices such as mmc or ata but it reports and error when spi
> > > flash is not present.
> > >
> > > Only print a notice that the storage device is missing when no response
> > > to the identify command is received.
> > >
> > > Consider reply buffers with all bits set to the same value no response.
> >
> > I'm not sure you can compare SPI with ATA and MMC. I'm just speaking 
> > of
> > DT now, but there, for ATA and MMC you just describe the controller 
> > and
> > it will auto-detect the connected storage. Whereas with SPI you 
> > describe
>
> Why does mmc assume storage and SDIO must be descibed? Why the special
> casing?

I can't follow you here. My SDIO wireless card just works in an SD
slot and doesn't have to be described.

> > both the controller and the flash. So I'd argue that your hardware
> > description is wrong if it describes a flash which is not present.
>
> At any rate the situation is the same - the storage may be present
> sometimes. I don't think assuming some kind of device by defualt is a
> sound practice.

Where is the assumption when the DT tells you there is a flash
on a specific chip select but actually there it isn't. Shouldn't
the DT then be fixed?

Maybe I don't understand your problem. What are you trying to
solve? I mean this just demotes an error to an info message.

> However, when the board is designed for a specific kind of device which
> is not always present, and the kernel can detect the device, it is
> perfectly fine to describe it.
>
> The alternative is to not use the device at all, even when present,
> which is kind of useless.

Or let the bootloader update your device tree and disable the device
if it's not there? Or load an overlay if it is there?

-michael