On 10/22/2015 10:14 AM, Arnd Bergmann 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 <appa...@xilinx.com> > > 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. > > If there are barriers that you want to get rid of for performance reasons, > you should use writel_relaxed(), but be careful to synchronize them correctly > with regard to DMA. It should be fine in this driver, as it does not > perform any DMA, but be aware that there is no big-endian version of > writel_relaxed() at the moment.
We don't have DMA in CAN drivers, but usually a certain write triggers sending. Do we need a barrier before triggering the sending? Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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