linux-kernel - RFC: arch: shall we have generic readl_be()/writel_be()/... or in_be32()/out

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Message-ID: <da9cb964-18a7-bff1-1249-b0df24daa05e@metux.net>
Date:   Wed, 9 Dec 2020 12:08:51 +0100
From:   "Enrico Weigelt, metux IT consult" <info@...ux.net>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arch@...r.kernel.org, linux-usb@...r.kernel.org,
        stern@...land.harvard.edu
Subject: RFC: arch: shall we have generic readl_be()/writel_be()/... or
 in_be32()/out_be32() ?

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 ?


thanks,

--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287