Re: RFC: arch: shall we have generic readl_be()/writel_be()/... or in_be32()/out_be32() ?
From: Alan Stern
Date: Wed Dec 09 2020 - 15:21:32 EST
On Wed, Dec 09, 2020 at 12:08:51PM +0100, Enrico Weigelt, metux IT consult wrote:
> Hello folks,
>
>
> while trying to make some more drivers compile-test'able, i've
> discovered some arch specific calls in here, eg.:
>
>
> In file included from
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci-spear.c:23:
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:
> In function 'ehci_readl':
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:743:3:
> error: implicit declaration of function 'readl_be'; did you mean
> 'readsb'? [-Werror=implicit-function-declaration]
> 743 | readl_be(regs) :
> | ^~~~~~~~
> | readsb
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:
> In function 'ehci_writel':
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:767:3:
> error: implicit declaration of function 'writel_be'; did you mean
> 'writesb'? [-Werror=implicit-function-declaration]
> 767 | writel_be(val, regs) :
> | ^~~~~~~~~
> | writesb
> In file included from
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci-hcd.c:97:
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:
> In function 'ehci_readl':
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:743:3:
> error: implicit declaration of function 'readl_be'; did you mean
> 'readsb'? [-Werror=implicit-function-declaration]
> 743 | readl_be(regs) :
> | ^~~~~~~~
> | readsb
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:
> In function 'ehci_writel':
> /home/nekrad/src/apu2-dev/pkg/kernel.apu2.git/drivers/usb/host/ehci.h:767:3:
> error: implicit declaration of function 'writel_be'; did you mean
> 'writesb'? [-Werror=implicit-function-declaration]
> 767 | writel_be(val, regs) :
> | ^~~~~~~~~
> | writesb
>
>
> It seems that only few archs (microblaze, ppc, sparc) define them.
>
> Also drivers/usb/host/ehci.h defines them, but only for one particular
> arch/subarch.
>
> IIRC, these funcs are for accessing hw registers that are in BEs, so
> BE cpus can do direct access, while LE cpus need to do a conversion.
>
> OTOH, we also have in_be32() / out_be32. They seem to do quite the same
> thing, referenced much more often, but also just defined on a few archs.
>
>
> I believe we should have generic functions, that all archs implement
> (possibly doing automatic conversion, if necessary), which are used
> by everybody else.
>
> What's your oppionion on that ?
It certainly seems reasonable. Another possibility, less stringent, is
to require that definitions exist on all architectures that can have
big-endian MMIO (or port-based IO). For example, any architecture
which might select CONFIG_EHCI_BIG_ENDIAN_MMIO, as used in ehci.h.
Otherwise we're left in the unfortunate position of having to provide
definitions for these functions, but _only_ on architectures that don't
already make their own definitions -- basically an impossible task.
Alan Stern