Subject: Re: [PATCH 1/2] can: xilinx: use readl/writel instead of ioread/iowrite

From: Michal Simek <[email-masked]>
Date: Thu, 22 Oct 2015 11:49:53 +0200

On 10/22/2015 11:02 AM, Arnd Bergmann wrote:
> On Thursday 22 October 2015 08:34:53 Appana Durga Kedareswara Rao wrote:
>>> On Thursday 22 October 2015 10:16:02 Kedareswara rao Appana wrote:
>>>> The driver only supports memory-mapped I/O [by ioremap()], so
>>>> readl/writel is actually the right thing to do, IMO.
>>>> During the validation of this driver or IP on ARM 64-bit processor
>>>> while sending lot of packets observed that the tx packet drop with
>>>> iowrite Putting the barriers for each tx fifo register write fixes
>>>> this issue Instead of barriers using writel also fixed this issue.
>>>>
>>>> Signed-off-by: Kedareswara rao Appana <[email-masked]>
>>>
>>> The two should really do the same thing: iowrite32() is just a static inline calling
>>> writel() on both ARM32 and ARM64. On which kernel version did you observe the
>>> difference? It's possible that an older version used CONFIG_GENERIC_IOMAP,
>>> which made this slightly more expensive.
>>
>> I observed this issue with the 4.0.0 kernel version
> 
> Is it possible that you have nonstandard patches on your kernel? If so, can
> you send a diff against the mainline version?

Kedar: Can you please retest this on mainline kernel?
We shouldn't have any patches which should influence this.

Thanks,
Michal