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

On 10/22/2015 11:02 AM, Arnd Bergmann wrote:

On Thursday 22 October 2015 08:34:53 Appana Durga Kedareswara Rao wrote:

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On Thursday 22 October 2015 10:16:02 Kedareswara rao Appana wrote:

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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 <redacted>

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