From: Lada Trimasova <Lada.Trimasova@synopsys.com>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"noamc@ezchip.com" <noamc@ezchip.com>,
Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>
Subject: Re: [PATCH] arc: use little endian accesses
Date: Thu, 10 Mar 2016 18:57:48 +0000 [thread overview]
Message-ID: <1457636268.457.34.camel@synopsys.com> (raw)
In-Reply-To: <C2D7FE5348E1B147BCA15975FBA23075F4E8F1A0@us01wembx1.internal.synopsys.com>
Hi Vineet, Alexey, Arnd,
On Thu, 2016-03-10 at 09:55 +0000, Vineet Gupta wrote:
Can you or Lada provide more details as to exactly what is not working - what
driver to be precise 8250 or dw-8250.
And where exactly the failure shows up. I want to understand this more
Noam told me off list that he has no issues with both big endian ARC + 8250 in
systemc model or silicon.
-Vineet
Driver is 8250, kernel is built for BE arc, nsim option in model "nsim_isa_big_endian = 1".
With current "readl" and "writel" implementation for ARC we read word from memory without any endianess manipulation. So in case of little endian architecture we get what we want: the first memory byte is the low byte in the word. But in case of big endian architecture the word endianess is swapped: the first memory byte is the high word byte.
And for example, let's see what happens when we use "readl" in function "serial8250_early_in" in driver/tty/serial/8250.
Take a look to one line from memory dump:
0xf0000010: 0x0b 0x00 0x00 0x00 0x60 0x00 0x00 0x00
When kernel is built for little endian architecture, we read this data in status register in function "serial_putc" using "readl" function in driver/tty/serial/8250 as:
r0: 0x0000006
The low byte is 0x0b, so the condition "if ((status & BOTH_EMPTY) == BOTH_EMPTY)" is true, as BOTH_EMPTY is some mask with low bytes set.
When kernel is built with "CPU_BIG_ENDIAN" and model nsim option is "nsim_isa_big_endian=1", we read this data as:
r0: 0x6000000
So as you can see the low byte is 0x00 and above mentioned condition never becomes true, we can't continue initialization.
Regards,
Lada
next prev parent reply other threads:[~2016-03-10 18:58 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-09 17:21 [PATCH] arc: use little endian accesses Lada Trimasova
2016-03-10 5:05 ` Vineet Gupta
2016-03-10 5:19 ` Vineet Gupta
2016-03-10 7:44 ` Alexey Brodkin
2016-03-10 9:55 ` Vineet Gupta
2016-03-10 18:57 ` Lada Trimasova [this message]
2016-03-10 19:23 ` Arnd Bergmann
2016-03-11 12:44 ` Vineet Gupta
2016-03-12 4:20 ` Vineet Gupta
2016-03-11 5:07 ` Noam Camus
2016-03-10 7:45 ` Arnd Bergmann
2016-03-11 5:18 ` Vineet Gupta
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1457636268.457.34.camel@synopsys.com \
--to=lada.trimasova@synopsys.com \
--cc=Alexey.Brodkin@synopsys.com \
--cc=Vineet.Gupta1@synopsys.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-snps-arc@lists.infradead.org \
--cc=noamc@ezchip.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).