[PATCH] ARM: kernel: Fix interrupted SMC calls

[Manivannan Sadhasivam]

On Qualcomm ARM32 platforms, the SMC call can return before it has
completed. If this occurs, the call can be restarted, but it requires
using the returned session ID value from the interrupted SMC call.

The ARM32 SMCC code already has the provision to add platform specific
quirks for things like this. So let's make use of it and add the
Qualcomm specific quirk (ARM_SMCCC_QUIRK_QCOM_A6) used by the QCOM_SCM
driver.

This change is similar to the below one added for ARM64 a while ago:
commit 82bcd087029f ("firmware: qcom: scm: Fix interrupted SCM calls")

Without this change, the Qualcomm ARM32 platforms like SDX55 will return
-EINVAL for SMC calls used for modem firmware loading and validation.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam at linaro.org>
---
 arch/arm/kernel/asm-offsets.c |  3 +++
 arch/arm/kernel/smccc-call.S  | 12 +++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index a1570c8bab25..2e2fa6fc2d4f 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -23,6 +23,7 @@
 #include <asm/vdso_datapage.h>
 #include <asm/hardware/cache-l2x0.h>
 #include <linux/kbuild.h>
+#include <linux/arm-smccc.h>
 #include "signal.h"
 
 /*
@@ -147,6 +148,8 @@ int main(void)
   DEFINE(SLEEP_SAVE_SP_PHYS,	offsetof(struct sleep_save_sp, save_ptr_stash_phys));
   DEFINE(SLEEP_SAVE_SP_VIRT,	offsetof(struct sleep_save_sp, save_ptr_stash));
 #endif
+  DEFINE(ARM_SMCCC_QUIRK_ID_OFFS,	offsetof(struct arm_smccc_quirk, id));
+  DEFINE(ARM_SMCCC_QUIRK_STATE_OFFS,	offsetof(struct arm_smccc_quirk, state));
   BLANK();
   DEFINE(DMA_BIDIRECTIONAL,	DMA_BIDIRECTIONAL);
   DEFINE(DMA_TO_DEVICE,		DMA_TO_DEVICE);
diff --git a/arch/arm/kernel/smccc-call.S b/arch/arm/kernel/smccc-call.S
index 00664c78faca..e1ab00b8244b 100644
--- a/arch/arm/kernel/smccc-call.S
+++ b/arch/arm/kernel/smccc-call.S
@@ -3,7 +3,9 @@
  * Copyright (c) 2015, Linaro Limited
  */
 #include <linux/linkage.h>
+#include <linux/arm-smccc.h>
 
+#include <asm/asm-offsets.h>
 #include <asm/opcodes-sec.h>
 #include <asm/opcodes-virt.h>
 #include <asm/unwind.h>
@@ -27,10 +29,18 @@ UNWIND(	.fnstart)
 UNWIND(	.save	{r4-r7})
 	ldm	r12, {r4-r7}
 	\instr
+	mov	r9, r6			// Copy r6 before popping from stack
 	pop	{r4-r7}
 	ldr	r12, [sp, #(4 * 4)]
 	stm	r12, {r0-r3}
-	bx	lr
+	ldr	r10, [sp, #20]
+	cmp	r10, #0
+	beq	1f			// No quirk structure
+	ldr     r11, [r10, #ARM_SMCCC_QUIRK_ID_OFFS]
+	cmp     r11, #ARM_SMCCC_QUIRK_QCOM_A6
+	bne	1f			// No quirk present
+	str	r9, [r10, #ARM_SMCCC_QUIRK_STATE_OFFS]
+1:	bx	lr
 UNWIND(	.fnend)
 	.endm
 
-- 
2.25.1