[PATCH v2] 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>
---

Changes in v2:

* Preserved callee saved registers and used the registers r4, r5 which
  are getting pushed onto the stack.

 arch/arm/kernel/asm-offsets.c |  3 +++
 arch/arm/kernel/smccc-call.S  | 11 ++++++++++-
 2 files changed, 13 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..931df62a7831 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>
@@ -27,7 +29,14 @@ UNWIND(	.fnstart)
 UNWIND(	.save	{r4-r7})
 	ldm	r12, {r4-r7}
 	\instr
-	pop	{r4-r7}
+	ldr	r4, [sp, #36]
+	cmp	r4, #0
+	beq	1f			// No quirk structure
+	ldr     r5, [r4, #ARM_SMCCC_QUIRK_ID_OFFS]
+	cmp     r5, #ARM_SMCCC_QUIRK_QCOM_A6
+	bne	1f			// No quirk present
+	str	r6, [r4, #ARM_SMCCC_QUIRK_STATE_OFFS]
+1:	pop	{r4-r7}
 	ldr	r12, [sp, #(4 * 4)]
 	stm	r12, {r0-r3}
 	bx	lr
-- 
2.25.1