linux-kernel - [PATCH 4/6] MIPS: fw: arc: workaround 64bit kernel/32bit ARC problems

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Date:   Wed,  9 Oct 2019 15:27:15 +0200
From:   Thomas Bogendoerfer <tbogendoerfer@...e.de>
To:     Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] MIPS: fw: arc: workaround 64bit kernel/32bit ARC problems

Pointer arguments for 32bit ARC PROMs must reside in CKSEG0/1. While
the initial stack resides in CKSEG0 the first kernel thread stack
is already placed at a XKPHYS address, which ARC32 can't handle.
The workaround here is to use static variables, which are placed
into BSS and linked to a CKSEG0 address.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@...e.de>
---
 arch/mips/fw/arc/promlib.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/mips/fw/arc/promlib.c b/arch/mips/fw/arc/promlib.c
index be381307fbb0..5e9e840a9314 100644
--- a/arch/mips/fw/arc/promlib.c
+++ b/arch/mips/fw/arc/promlib.c
@@ -11,6 +11,21 @@
 #include <asm/bcache.h>
 #include <asm/setup.h>
 
+#if defined(CONFIG_64BIT) && defined(CONFIG_FW_ARC32)
+/*
+ * For 64bit kernels working with a 32bit ARC PROM pointer arguments
+ * for ARC calls need to reside in CKEG0/1. But as soon as the kernel
+ * switches to it's first kernel thread stack is set to an address in
+ * XKPHYS, so anything on stack can't be used anymore. This is solved
+ * by using a * static declartion variables are put into BSS, which is
+ * linked to a CKSEG0 address. Since this is only used on UP platforms
+ * there is not spinlock needed
+ */
+#define O32_STATIC	static
+#else
+#define O32_STATIC
+#endif
+
 /*
  * IP22 boardcache is not compatible with board caches.	 Thus we disable it
  * during romvec action.  Since r4xx0.c is always compiled and linked with your
@@ -23,8 +38,10 @@
 
 void prom_putchar(char c)
 {
-	ULONG cnt;
-	CHAR it = c;
+	O32_STATIC ULONG cnt;
+	O32_STATIC CHAR it;
+
+	it = c;
 
 	bc_disable();
 	ArcWrite(1, &it, 1, &cnt);
@@ -33,8 +50,8 @@ void prom_putchar(char c)
 
 char prom_getchar(void)
 {
-	ULONG cnt;
-	CHAR c;
+	O32_STATIC ULONG cnt;
+	O32_STATIC CHAR c;
 
 	bc_disable();
 	ArcRead(0, &c, 1, &cnt);
-- 
2.16.4