RFC on writel and writel_relaxed

Sinan Kaya okaya at codeaurora.org
Fri Mar 30 03:59:23 AEDT 2018

On 3/29/2018 12:29 PM, Arnd Bergmann wrote:
> On Thu, Mar 29, 2018 at 3:56 PM, Sinan Kaya <okaya at codeaurora.org> wrote:
>> On 3/28/2018 11:55 AM, David Miller wrote:
>>> From: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>>> Date: Thu, 29 Mar 2018 02:13:16 +1100
>>>> Let's fix all archs, it's way easier than fixing all drivers. Half of
>>>> the archs are unused or dead anyway.
>>> Agreed.
>> I pinged most of the maintainers yesterday.
>> Which arches do we care about these days?
>> I have not been paying attention any other architecture besides arm64.
>> arch            status                  detail
>> ------          -------------           ------------------------------------
>> alpha           question sent

Thanks for the detailed analysis.

> I'm guessing alpha has problems
> extern inline u32 readl(const volatile void __iomem *addr)
> {
>         u32 ret = __raw_readl(addr);
>         mb();
>         return ret;
> }
> extern inline void writel(u32 b, volatile void __iomem *addr)
> {
>         __raw_writel(b, addr);
>         mb();
> }

Looks like a problem to me too. I'll start a thread with the alpha
people and CC you.

> There is a barrier in writel /after/ the acess but not before.

This is the consolidated list. I also heart back from m68k and corrected
contacts for arc and h8300.

arch            status                  detail
------          -------------           ------------------------------------
alpha		question sent		Arnd: alpha has problems
arc		question sent		Vineet.Gupta1 at synopsys.com says he'll get to this
					in the next few days
arm		no issues
arm64		no issues
c6x		no issues		no PCI
h8300		no issues		no PCI: ysato at users.sourceforge.jp will fix it.
hexagon		no issues		no PCI
ia64		no issues		confirmed by Tony Luck
m68k		no issues		geert at linux-m68k.org says no problem
metag		no issues		arnd: removed
microblaze	question sent		arnd: some mips platforms have problems
mips		question sent		arnd: some mips platforms have problems
nds32		question sent
nios2		no issues		no PCI
openrisc	no issues		shorne at gmail.com says should no issues
parisc		no issues		grantgrundler at gmail.com says most probably no problem
					but still looking
powerpc		no issues
riscv		no issues		arnd: riscv should be fine
s390		no issues		arnd: Pretty sure this is also fine
sh		question sent
sparc		no issues		davem at davemloft.net says always strongly ordered
unicore32	question sent		resent to gxt at pku.edu.cn
x86		no issues
x86_64		no issues

>          Arnd

Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

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