linux-kernel - Re: [PATCH 00/16 v9] omap 8250 based uart + DMA

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Date:	Wed, 17 Sep 2014 10:38:52 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Tony Lindgren <tony@...mide.com>
CC:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	balbi@...com, gregkh@...uxfoundation.org
Subject: Re: [PATCH 00/16 v9] omap 8250 based uart + DMA

On 09/16/2014 11:30 PM, Tony Lindgren wrote:
> Found one more issue when booting on 2420 n8x0, maybe something to do
> with runtime PM?
To some degree, yes.

> [    4.770507] Internal error: Oops - undefined instruction: 0 [#1]
SMP ARM

  e3a02000        mov     r2, #0
  ee072fba        mcr     15, 0, r2, cr7, cr10, {5}
  e3a01001        mov     r1, #1
  f5d3f000        pld     [r3]
=>e1d30f9f        ldrexb  r0, [r3]

That ldrexb is part of the xchg() function in serial8250_rpm_get_tx().
So it looks like 2420 n8x0 does not understand ldrexb but the inline
assembly decided that it should.

This OMAP2420 should be ARM1136 / ARMv6. The ARM1136J(F)-S TRM says for
ldrexb: "This command is only available from the rev1 (r1p0) release of
the ARM1136JF-S processor."

So it looks like the CPU should know what to do when this opcode comes
around.

> 
> Regards,
> 
> Tony
> 

Sebastian
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