[PATCH] powerpc/mpc52xx/mtd: fix mtd-ram access for 16-bit Local Plus Bus

["Albrecht Dreß" <albrecht.dress@arcor.de>]

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Hi all,

this patch adds support for RAM chips connected to the Local Plus Bus  
of a MPC5200B in 16-bit mode.  As no single byte write accesses are  
allowed by the bus in this mode, a byte write has to be split into a  
word read - modify - write sequence (mpc52xx_memcpy2lpb16, as  
fix/extension for memcpy_toio; note that memcpy_fromio *does* work just  
fine).  It has been tested in conjunction with Wolfram Sang's mtd-ram  
[1] and Sascha Hauer's jffs unaligned access [2] patches on 2.6.29.1,  
with a Renesas static RAM connected in 16-bit "Large Flash" mode.

[1]  
<http://lists.ozlabs.org/pipermail/linuxppc-dev/2009-June/072794.html>
[2] <http://article.gmane.org/gmane.linux.drivers.mtd/21521>

Signed-off-by: Albrecht Dreß <albrecht.dress@arcor.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: linuxppc-dev@ozlabs.org

---

diff -u  
linux-2.6.29.1.orig/arch/powerpc/platforms/52xx/mpc52xx_common.c  
linux-2.6.29.1/arch/powerpc/platforms/52xx/mpc52xx_common.c
--- linux-2.6.29.1.orig/arch/powerpc/platforms/52xx/mpc52xx_common.c     
2009-04-02 22:55:27.000000000 +0200
+++ linux-2.6.29.1/arch/powerpc/platforms/52xx/mpc52xx_common.c  
2009-06-09 21:16:22.000000000 +0200
@@ -225,3 +225,59 @@

         while (1);
  }
+
+/**
+ * mpc52xx_memcpy2lpb16: copy data to the Local Plus Bus in 16-bit  
mode which
+ * doesn't allow byte accesses
+ */
+void
+mpc52xx_memcpy2lpb16(volatile void __iomem *dest, const void *src,
+                    unsigned long n)
+{
+       void *vdest = (void __force *) dest;
+
+       __asm__ __volatile__ ("sync" : : : "memory");
+
+       if (((unsigned long) vdest & 1) != 0) {
+               u8 buf[2];
+
+               *(u16 *)buf = *((volatile u16 *)(vdest - 1));
+               buf[1] = *((u8 *)src);
+               *((volatile u16 *)(vdest - 1)) = *(u16 *)buf;
+               src++;
+               vdest++;
+               n--;
+       }
+
+       /* looks weird, but helps the optimiser... */
+       if (n >= 4) {
+               unsigned long chunks = n >> 2;
+               volatile u32 * _dst = (volatile u32 *)(vdest - 4);
+               volatile u32 * _src = (volatile u32 *)(src - 4);
+
+               vdest += chunks << 2;
+               src += chunks << 2;
+               do {
+                       *++_dst = *++_src;
+               } while (--chunks);
+               n &= 3;
+       }
+
+       if (n >= 2) {
+               *((volatile u16 *)vdest) = *((volatile u16 *)src);
+               src += 2;
+               vdest += 2;
+               n -= 2;
+       }
+
+       if (n > 0) {
+               u8 buf[2];
+
+               *(u16 *)buf = *((volatile u16 *)vdest);
+               buf[0] = *((u8 *)src);
+               *((volatile u16 *)vdest) = *(u16 *)buf;
+       }
+
+       __asm__ __volatile__ ("sync" : : : "memory");
+}
+EXPORT_SYMBOL(mpc52xx_memcpy2lpb16);
diff -u linux-2.6.29.1.orig/arch/powerpc/include/asm/mpc52xx.h  
linux-2.6.29.1/arch/powerpc/include/asm/mpc52xx.h
--- linux-2.6.29.1.orig/arch/powerpc/include/asm/mpc52xx.h       
2009-04-02 22:55:27.000000000 +0200
+++ linux-2.6.29.1/arch/powerpc/include/asm/mpc52xx.h   2009-06-09  
21:14:31.000000000 +0200
@@ -274,6 +274,8 @@
  extern void mpc52xx_map_common_devices(void);
  extern int mpc52xx_set_psc_clkdiv(int psc_id, int clkdiv);
  extern void mpc52xx_restart(char *cmd);
+extern void mpc52xx_memcpy2lpb16(volatile void __iomem *dest, const  
void *src,
+                                unsigned long n);

  /* mpc52xx_pic.c */
  extern void mpc52xx_init_irq(void);
diff -u linux-2.6.29.1.orig/include/linux/mtd/map.h  
linux-2.6.29.1/include/linux/mtd/map.h
--- linux-2.6.29.1.orig/include/linux/mtd/map.h 2009-04-02  
22:55:27.000000000 +0200
+++ linux-2.6.29.1/include/linux/mtd/map.h      2009-06-08  
14:28:05.000000000 +0200
@@ -13,6 +13,9 @@
  #include <asm/unaligned.h>
  #include <asm/system.h>
  #include <asm/io.h>
+#ifdef CONFIG_PPC_MPC52xx
+#include <asm/mpc52xx.h>
+#endif

  #ifdef CONFIG_MTD_MAP_BANK_WIDTH_1
  #define map_bankwidth(map) 1
@@ -417,6 +420,11 @@

  static inline void inline_map_copy_to(struct map_info *map, unsigned  
long to, const void *from, ssize_t len)
  {
+#ifdef CONFIG_PPC_MPC52xx
+       if (map->bankwidth == 2)
+               mpc52xx_memcpy2lpb16(map->virt + to, from, len);
+       else
+#endif
         memcpy_toio(map->virt + to, from, len);
  }


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