linux-kernel - Re: [PATCH v3 1/5] io: define several IO & PIO barrier types for the asm-generic version

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Date:   Thu, 05 Apr 2018 07:48:36 -0400
From:   okaya@...eaurora.org
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Timur Tabi <timur@...eaurora.org>, sulrich@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        arndbergmann@...il.com
Subject: Re: [PATCH v3 1/5] io: define several IO & PIO barrier types for the
 asm-generic version

On 2018-04-05 03:00, Arnd Bergmann wrote:
> On Thu, Apr 5, 2018 at 1:58 AM, Sinan Kaya <okaya@...eaurora.org> 
> wrote:
> 
> Looks good, but I'd change the comments to ones that document exactly
> what those barriers are for:
> 
>> +#ifndef __io_ar
>> +#ifdef rmb
>> +/* prefer rmb() as the default implementation of __io_ar() if 
>> supported */
>> +#define __io_ar()      rmb()
> 
> /*
>  * prevent prefetching of coherent DMA data ahead of a dma-complete */
> 
>> +#ifndef __io_bw
>> +#ifdef wmb
>> +/* prefer wmb() as the default implementation of __io_bw() if 
>> supported */
>> +#define __io_bw()      wmb()
>> +#else
> 
> /* flush writes to coherent DMA data before possibly triggering a DMA 
> read */
> 
>> +#ifndef __io_aw
>> +#define __io_aw()      barrier()
>> +#endif
> 
> /* serialize device access against a spin_unlock, usually handled there 
> */
> 

I will add these and post the next version.

> The other four patches look perfect already.  What's the timing we need 
> for
> these patches? Are they 4.18 material, or do we need them in 4.17 and
> stable kernels to work around known bugs?

I was hoping to get all arch stuff in for 4.17.

Driver developers started removing redundant wmb().

> 
>       Arnd