netdev - Re: RFC on writel and writel

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Message-ID: <48b2698a-8cc6-22c5-551c-88e84cc06a71@codeaurora.org>
Date:   Thu, 29 Mar 2018 12:59:23 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     David Miller <davem@...emloft.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Will Deacon <will.deacon@....com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        David Laight <David.Laight@...lab.com>,
        Oliver O'Halloran <oohall@...il.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Alexander Duyck <alexander.h.duyck@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Networking <netdev@...r.kernel.org>,
        Linus Torvalds <linus971@...il.com>
Subject: Re: RFC on writel and writel_relaxed

On 3/29/2018 12:29 PM, Arnd Bergmann wrote:
> On Thu, Mar 29, 2018 at 3:56 PM, Sinan Kaya <okaya@...eaurora.org> wrote:
>> On 3/28/2018 11:55 AM, David Miller wrote:
>>> From: Benjamin Herrenschmidt <benh@...nel.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@...opsys.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@...rs.sourceforge.jp will fix it.
hexagon		no issues		no PCI
ia64		no issues		confirmed by Tony Luck
m68k		no issues		geert@...ux-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@...il.com says should no issues
parisc		no issues		grantgrundler@...il.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@...emloft.net says always strongly ordered
unicore32	question sent		resent to gxt@....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.