Hi Arnd, > -----Original Message----- > From: Arnd Bergmann [mailto:a...@arndb.de] > Sent: Thursday, October 22, 2015 1:45 PM > To: linux-arm-ker...@lists.infradead.org > Cc: Appana Durga Kedareswara Rao; Anirudha Sarangi; w...@grandegger.com; > m...@pengutronix.de; Michal Simek; Soren Brinkmann; Appana Durga > Kedareswara Rao; net...@vger.kernel.org; linux-kernel@vger.kernel.org; linux- > c...@vger.kernel.org > Subject: Re: [PATCH 1/2] can: xilinx: use readl/writel instead of > ioread/iowrite > > 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.
I observed this issue with the 4.0.0 kernel version > > 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. There is no DMA in CAN for this IP. Regards, Kedar. > > Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
