linux-kernel - Re: [PATCH 1/2] ARM: build ssi-fiq.S in ARM mode to prevent CONFIG_THUMB2

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Message-ID: <20120809102414.GA17588@linaro.org>
Date:	Thu, 9 Aug 2012 11:24:14 +0100
From:	Dave Martin <dave.martin@...aro.org>
To:	Matt Sealey <matt@...esi-usa.com>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	Linux ARM Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>,
	Steev Klimaszewski <steev@...esi-usa.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH 1/2] ARM: build ssi-fiq.S in ARM mode to prevent
 CONFIG_THUMB2_KERNEL build breakage

On Wed, Aug 08, 2012 at 12:32:39PM -0500, Matt Sealey wrote:

[...]
 
> I'm going to do a trapse through and find where Russell nacked Dave's
> thumb-aware
> rewrite.. would you mind if you have any of these boards seeing if it
> really DOES

There was no NAK because I didn't get as far as posting the patch,
mostly because of the doubt about whether this code is ever relevant
on Thumb2-capable hardware.

If somebody with some old imx hardware that definitely relies on this
wants to pick it up and test it, it might still be useful.

I don't know whether I still have the original patch, but I think the
only think I did was to swap the roles of r13 and r12.  In the original
code r12 is only used as a base register, which is permissible usage
for r13 in Thumb-2.  Those two registers appear private to the fiq
handler, so I don't think the change will break anything, but I'd be
more confident is somebody is able to test it.

Cheers
---Dave

diff --git a/arch/arm/plat-mxc/ssi-fiq.S b/arch/arm/plat-mxc/ssi-fiq.S
index 8397a2d..3589afb 100644
--- a/arch/arm/plat-mxc/ssi-fiq.S
+++ b/arch/arm/plat-mxc/ssi-fiq.S
@@ -35,19 +35,19 @@
 		.global imx_ssi_fiq_tx_buffer
 
 imx_ssi_fiq_start:
-		ldr r12, imx_ssi_fiq_base
+		ldr r13, imx_ssi_fiq_base
 
 		/* TX */
 		ldr r11, imx_ssi_fiq_tx_buffer
 
 		/* shall we send? */
-		ldr r13, [r12, #SSI_SIER]
-		tst r13, #SSI_SIER_TFE0_EN
+		ldr r12, [r13, #SSI_SIER]
+		tst r12, #SSI_SIER_TFE0_EN
 		beq 1f
 
 		/* TX FIFO empty? */
-		ldr r13, [r12, #SSI_SISR]
-		tst r13, #SSI_SISR_TFE0
+		ldr r12, [r13, #SSI_SISR]
+		tst r12, #SSI_SISR_TFE0
 		beq 1f
 
 		mov r10, #0x10000
@@ -56,34 +56,34 @@ imx_ssi_fiq_start:
 
 		add r11, r11, r10
 
-		ldrh r13, [r11]
-		strh r13, [r12, #SSI_STX0]
+		ldrh r12, [r11]
+		strh r12, [r13, #SSI_STX0]
 
-		ldrh r13, [r11, #2]
-		strh r13, [r12, #SSI_STX0]
+		ldrh r12, [r11, #2]
+		strh r12, [r13, #SSI_STX0]
 
-		ldrh r13, [r11, #4]
-		strh r13, [r12, #SSI_STX0]
+		ldrh r12, [r11, #4]
+		strh r12, [r13, #SSI_STX0]
 
-		ldrh r13, [r11, #6]
-		strh r13, [r12, #SSI_STX0]
+		ldrh r12, [r11, #6]
+		strh r12, [r13, #SSI_STX0]
 
 		add r10, #8
-		lsr r13, r8, #16	/* r13: buffer size */
-		cmp r10, r13
-		lslgt r8, r13, #16
+		lsr r12, r8, #16	/* r12: buffer size */
+		cmp r10, r12
+		lslgt r8, r12, #16
 		addle r8, #8
 1:
 		/* RX */
 
 		/* shall we receive? */
-		ldr r13, [r12, #SSI_SIER]
-		tst r13, #SSI_SIER_RFF0_EN
+		ldr r12, [r13, #SSI_SIER]
+		tst r12, #SSI_SIER_RFF0_EN
 		beq 1f
 
 		/* RX FIFO full? */
-		ldr r13, [r12, #SSI_SISR]
-		tst r13, #SSI_SISR_RFF0
+		ldr r12, [r13, #SSI_SISR]
+		tst r12, #SSI_SISR_RFF0
 		beq 1f
 
 		ldr r11, imx_ssi_fiq_rx_buffer
@@ -94,31 +94,31 @@ imx_ssi_fiq_start:
 
 		add r11, r11, r10
 
-		ldr r13, [r12, #SSI_SACNT]
-		tst r13, #SSI_SACNT_AC97EN
+		ldr r12, [r13, #SSI_SACNT]
+		tst r12, #SSI_SACNT_AC97EN
 
-		ldr r13, [r12, #SSI_SRX0]
-		strh r13, [r11]
+		ldr r12, [r13, #SSI_SRX0]
+		strh r12, [r11]
 
-		ldr r13, [r12, #SSI_SRX0]
-		strh r13, [r11, #2]
+		ldr r12, [r13, #SSI_SRX0]
+		strh r12, [r11, #2]
 
 		/* dummy read to skip slot 12 */
-		ldrne r13, [r12, #SSI_SRX0]
+		ldrne r12, [r13, #SSI_SRX0]
 
-		ldr r13, [r12, #SSI_SRX0]
-		strh r13, [r11, #4]
+		ldr r12, [r13, #SSI_SRX0]
+		strh r12, [r11, #4]
 
-		ldr r13, [r12, #SSI_SRX0]
-		strh r13, [r11, #6]
+		ldr r12, [r13, #SSI_SRX0]
+		strh r12, [r11, #6]
 
 		/* dummy read to skip slot 12 */
-		ldrne r13, [r12, #SSI_SRX0]
+		ldrne r12, [r13, #SSI_SRX0]
 
 		add r10, #8
-		lsr r13, r9, #16	/* r13: buffer size */
-		cmp r10, r13
-		lslgt r9, r13, #16
+		lsr r12, r9, #16	/* r12: buffer size */
+		cmp r10, r12
+		lslgt r9, r12, #16
 		addle r9, #8
 
 1:

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