Re: [PATCH v7 09/10] um: Add dummy implementation for IO memcpy/memset

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2024-10-07 at 09:49 +0200, Julian Vetter wrote:
> 
> > > The um arch is the only architecture that sets the config 'NO_IOMEM',

(you did note this, for the comment below)

> No, I think you're understanding the series correctly. It doesn't work. 
> I will revert this.

OK.

> > You're adding these inlines unconditionally, so if this included
> > logic_io.h, you should get symbol conflicts?
> > 
> > Also not sure these functions should/need to do anything at all, there's
> > no IO memory on ARCH=um in case of not having logic_io.h. Maybe even
> > BUG_ON() or something? It can't be reachable (under correct drivers)
> > since ioremap() always returns NULL (without logic_iomem).

> Thanks. You're right. I added this patch because there was a build robot 
> on some mailinglist building a random config with 'ARCH=um' and with 
> some MTD drivers that actually use memcpy_fromio or memcpy_toio. These 
> drivers are not guarded by a 'depends on HAS_IOMEM'. I thought I could 
> simply fix it by adding stub functions to the um arch. Because I saw 
> there are A LOT of drivers that use IO functions without being guarded 
> by 'depends on HAS_IOMEM'. Not sure though, how to handle this case.

Right, well, as you noted above ARCH=um is the only architecture that
has NO_IOMEM, so I suppose drivers are just broken. But e.g.
kernel/iomem.c is also only ever built if you have HAS_IOMEM, so devm_*
functions related to this are not available.

So I don't know. On the one hand, it feels correct to have NO_IOMEM and
HAS_IOMEM, on the other hand that's a bit of a fight against windmills?


What happens now though? Seems it should _already_ not build with
ARCH=um and memcpy_*io() being used? No, I guess it picked up the asm-
generic version?

Hm. I'm almost thinking we should let such drivers not build, and then
see that they add appropriate HAS_IOMEM dependencies, but ... windmills?

johannes