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From: Stephen Warren <swarren@wwwdotorg.org>
To: Jongsung Kim <neidhard.kim@lge.com>
Cc: linux@arm.linux.org.uk, gregkh@linuxfoundation.org,
	jslaby@suse.cz, linux-serial@vger.kernel.org,
	linux-rpi-kernel@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ARM: bcm2835: override the HW UART periphid
Date: Tue, 21 May 2013 10:34:17 -0600	[thread overview]
Message-ID: <519BA209.6050407@wwwdotorg.org> (raw)
In-Reply-To: <1369116149-2361-1-git-send-email-neidhard.kim@lge.com>

On 05/21/2013 12:02 AM, Jongsung Kim wrote:
> Stephen Warren reported the recent commit 78506f2 (add support for
> extended FIFO-size of PL011-r1p5) breaks the serial port on the
> BCM2835 ARM SoC.
> 
> A UART compatible with the ARM PL011-r1p5 should have 32-deep FIFOs.
> The BCM2835 UART just looks like an ARM PL011-r1p5, but has 16-deep
> FIFOs just like PL011-r1p4 or earlier revisions. As a workaround for
> this compatibility issue, this patch overrides the HW UART periphid
> register values with the actually compatible UART periphid 0x00241011
> (r1p3 or r1p4).
> 
> Reported-by: Stephen Warren <swarren@wwwdotorg.org>
> Signed-off-by: Jongsung Kim <neidhard.kim@lge.com>

I know this will work, because I tried out the same thing last week.

However, I'm not convinced that it's the correct approach. What other
changes exist between r1p4 and r1p5; can you check in the TRM? Faking
the periphid would prevent the driver from taking account of any other
changes. Should we instead add a DT property solely to override the FIFO
size, and then set that for bcm2835? I guess if there really aren't any
other SW-visible changes in r1p5, this approach is fine.

WARNING: multiple messages have this Message-ID (diff)
From: swarren@wwwdotorg.org (Stephen Warren)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: bcm2835: override the HW UART periphid
Date: Tue, 21 May 2013 10:34:17 -0600	[thread overview]
Message-ID: <519BA209.6050407@wwwdotorg.org> (raw)
In-Reply-To: <1369116149-2361-1-git-send-email-neidhard.kim@lge.com>

On 05/21/2013 12:02 AM, Jongsung Kim wrote:
> Stephen Warren reported the recent commit 78506f2 (add support for
> extended FIFO-size of PL011-r1p5) breaks the serial port on the
> BCM2835 ARM SoC.
> 
> A UART compatible with the ARM PL011-r1p5 should have 32-deep FIFOs.
> The BCM2835 UART just looks like an ARM PL011-r1p5, but has 16-deep
> FIFOs just like PL011-r1p4 or earlier revisions. As a workaround for
> this compatibility issue, this patch overrides the HW UART periphid
> register values with the actually compatible UART periphid 0x00241011
> (r1p3 or r1p4).
> 
> Reported-by: Stephen Warren <swarren@wwwdotorg.org>
> Signed-off-by: Jongsung Kim <neidhard.kim@lge.com>

I know this will work, because I tried out the same thing last week.

However, I'm not convinced that it's the correct approach. What other
changes exist between r1p4 and r1p5; can you check in the TRM? Faking
the periphid would prevent the driver from taking account of any other
changes. Should we instead add a DT property solely to override the FIFO
size, and then set that for bcm2835? I guess if there really aren't any
other SW-visible changes in r1p5, this approach is fine.

  parent reply	other threads:[~2013-05-21 16:34 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-12  9:18 [PATCH] ARM: PL011: add support for extended FIFO-size of PL011-r1p5 Jongsung Kim
2013-04-12  9:18 ` Jongsung Kim
2013-04-19 12:58 ` Russell King - ARM Linux
2013-05-14  5:56 ` Stephen Warren
2013-05-14  5:56   ` Stephen Warren
2013-05-14  5:56   ` Stephen Warren
2013-05-14  7:15   ` Jongsung Kim
2013-05-14  7:15     ` Jongsung Kim
2013-05-14  7:15     ` Jongsung Kim
2013-05-14 21:03     ` Stephen Warren
2013-05-14 21:03       ` Stephen Warren
2013-05-14 22:50       ` Russell King - ARM Linux
2013-05-14 22:50         ` Russell King - ARM Linux
2013-05-15  1:00       ` Jongsung Kim
2013-05-15  1:00         ` Jongsung Kim
2013-05-15  1:00         ` Jongsung Kim
2013-05-15  4:59         ` Stephen Warren
2013-05-15  4:59           ` Stephen Warren
2013-05-15  9:37           ` Russell King - ARM Linux
2013-05-15  9:37             ` Russell King - ARM Linux
2013-05-16 13:26           ` Jongsung Kim
2013-05-16 13:26             ` Jongsung Kim
2013-05-16 13:26             ` Jongsung Kim
2013-05-21  1:39           ` Jongsung Kim
2013-05-21  1:39             ` Jongsung Kim
2013-05-21  1:39             ` Jongsung Kim
2013-05-21  2:12             ` Stephen Warren
2013-05-21  2:12               ` Stephen Warren
2013-05-21  6:02               ` [PATCH] ARM: bcm2835: override the HW UART periphid Jongsung Kim
2013-05-21  6:02                 ` Jongsung Kim
2013-05-21  6:07                 ` Jongsung Kim
2013-05-21  6:07                   ` Jongsung Kim
2013-05-21  6:07                   ` Jongsung Kim
2013-05-21  9:00                   ` Gordon Hollingworth
2013-05-21  9:00                     ` Gordon Hollingworth
2013-05-21  9:00                     ` Gordon Hollingworth
2013-05-21 16:34                 ` Stephen Warren [this message]
2013-05-21 16:34                   ` Stephen Warren
2013-05-22  1:43                   ` Stephen Warren
2013-05-22  1:43                     ` Stephen Warren
2013-05-22  1:52                     ` Jongsung Kim
2013-05-22  1:52                       ` Jongsung Kim
2013-05-22  1:52                       ` Jongsung Kim
2013-05-30  4:07 Stephen Warren
2013-06-01  6:43 ` Olof Johansson

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