linux-kernel - Re: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM

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Date:	Tue, 4 Jan 2011 10:52:56 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Nicolas Pitre <nico@...xnic.net>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>,
	Daniel Walker <dwalker@...eaurora.org>
Subject: Re: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM

* Nicolas Pitre <nico@...xnic.net> [101220 13:44]:
> On Mon, 20 Dec 2010, Stephen Boyd wrote:
> 
> > The inline assembly differences for v6 vs. v7 in the hvc_dcc
> > driver are purely optimizations. On a v7 processor, an mrc with
> > the pc sets the condition codes to the 28-31 bits of the register
> > being read. It just so happens that the TX/RX full bits the DCC
> > driver is testing for are high enough in the register to be put
> > into the condition codes. On a v6 processor, this "feature" isn't
> > implemented and thus we have to do the usual read, mask, test
> > operations to check for TX/RX full.
> > 
> > Since we already test the RX/TX full bits before calling
> > __dcc_getchar() and __dcc_putchar() we don't actually need to do
> > anything special for v7 over v6. The only difference is in
> > hvc_dcc_get_chars(). We would test RX full, poll RX full, and
> > then read a character from the buffer, whereas now we will test
> > RX full, read a character from the buffer, and then test RX full
> > again for the second iteration of the loop. It doesn't seem
> > possible for the buffer to go from full to empty between testing
> > the RX full and reading a character. Therefore, replace the v7
> > versions with the v6 versions and everything works the same.
> > 
> > Cc: Tony Lindgren <tony@...mide.com>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Nicolas Pitre <nicolas.pitre@...aro.org>
> > Cc: Daniel Walker <dwalker@...eaurora.org>
> > Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> 
> Acked-by: Nicolas Pitre <nicolas.pitre@...aro.org>

Acked-by: Tony Lindgren <tony@...mide.com>
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