linux-kernel - Re: [PATCH v4 5/5] zynq: move static peripheral mappings

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Message-ID: <20121026010303.GA13669@beefymiracle.amer.corp.natinst.com>
Date:	Thu, 25 Oct 2012 20:03:03 -0500
From:	Josh Cartwright <josh.cartwright@...com>
To:	Nick Bowler <nbowler@...iptictech.com>
Cc:	arm@...nel.org, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	John Linn <john.linn@...inx.com>,
	Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH v4 5/5] zynq: move static peripheral mappings

On Thu, Oct 25, 2012 at 06:41:08PM -0400, Nick Bowler wrote:
> On 2012-10-25 16:29 -0500, Josh Cartwright wrote:
> > On Thu, Oct 25, 2012 at 04:17:01PM -0400, Nick Bowler wrote:
> > > Did you test this on any real hardware?  I can't get the ZC702 to work
> > > with the UART mapped at this address (this ends up being mapped at
> > > 0xFEFFF000), although I can't for the life of me figure out why the
> > > virtual address even matters.  Note that for the ZC702, the physical
> > > address of the "main" UART is 0xE0001000.

Good news is you're not crazy; I was able to duplicate the problem here.

> If I were to guess, I would guess that, except for when it "Works",
> the really really early printk stuff isn't actually hitting the uart
> at all.  The "Fails" case would then be due to the stray writes
> crashing the board, and the "Truncated" case due to the stray writes
> being (ostensibly) benign.

If I'm not mistaken, this hypothesis is predicated on the early bootup
code establishing a (linear?) mapping for addresses > VMALLOC_START;
before the mdesc->map_io() is even handled.  That seems odd to me.

> But I really have no way right now to test this hypothesis, since I
> can't print anything in the failing case.

Not sure if I'll be able to get anything meaningful out of it yet (I've
not historically had good luck with Xilinx's debugging tools), but I did
finally get a JTAG debugger hooked up to the zc702.  I'll see if I can
get any useful information tomorrow.

Thanks,

  Josh

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