From: Arnd Bergmann <arnd@arndb•de>
To: linux-arm-kernel@lists•infradead.org
Cc: Appana Durga Kedareswara Rao <appana.durga.rao@xilinx•com>,
"netdev@vger•kernel.org" <netdev@vger•kernel.org>,
"linux-kernel@vger•kernel.org" <linux-kernel@vger•kernel.org>,
"linux-can@vger•kernel.org" <linux-can@vger•kernel.org>,
Michal Simek <michals@xilinx•com>,
Soren Brinkmann <sorenb@xilinx•com>,
Anirudha Sarangi <anirudh@xilinx•com>,
"mkl@pengutronix•de" <mkl@pengutronix•de>,
"wg@grandegger•com" <wg@grandegger•com>
Subject: Re: [PATCH 1/2] can: xilinx: use readl/writel instead of ioread/iowrite
Date: Thu, 22 Oct 2015 11:02:38 +0200 [thread overview]
Message-ID: <3847286.pUBWjpC1TL@wuerfel> (raw)
In-Reply-To: <C246CAC1457055469EF09E3A7AC4E11A4A4F2CDB@XAP-PVEXMBX01.xlnx.xilinx.com>
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 <appanad@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
Is it possible that you have nonstandard patches on your kernel? If so, can
you send a diff against the mainline version?
I don't see CONFIG_GENERIC_IOMAP in 4.0.0, and writel() definitely has the
necessary barriers on arm64, the same way that iowrite() does.
> > 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.
Ok, good.
Arnd
next prev parent reply other threads:[~2015-10-22 9:02 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-22 4:46 [PATCH 1/2] can: xilinx: use readl/writel instead of ioread/iowrite Kedareswara rao Appana
2015-10-22 4:46 ` [PATCH 2/2] can: xilinx: fix bug in bus error handling Kedareswara rao Appana
2015-10-22 4:46 ` Kedareswara rao Appana
2015-10-22 4:46 ` Kedareswara rao Appana
2015-10-22 8:14 ` [PATCH 1/2] can: xilinx: use readl/writel instead of ioread/iowrite Arnd Bergmann
2015-10-22 8:21 ` Marc Kleine-Budde
2015-10-22 8:39 ` Appana Durga Kedareswara Rao
2015-10-22 8:58 ` Arnd Bergmann
2015-10-25 20:32 ` Marc Kleine-Budde
2015-10-26 1:25 ` Arnd Bergmann
2015-10-22 8:34 ` Appana Durga Kedareswara Rao
2015-10-22 9:02 ` Arnd Bergmann [this message]
2015-10-22 9:49 ` Michal Simek
[not found] ` <1445489163-11045-2-git-send-email-appanad@xilinx.com>
2015-10-22 16:33 ` [PATCH 2/2] can: xilinx: fix bug in bus error handling Sören Brinkmann
2015-10-23 5:21 ` Appana Durga Kedareswara Rao
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