powerpc/mpc5200: Disable bestcomm prefetching when ATA DMA enabled

When ATA DMA is enabled, bestcomm prefetching does not work.  This
patch adds a function to disable bestcomm prefetch when the ATA
Bestcomm task is initialized.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

3 files changed, 21 insertions, 5 deletions

diff --git a/arch/powerpc/sysdev/bestcomm/ata.c b/arch/powerpc/sysdev/bestcomm/ata.c
index 1f5258fb38c3..901c9f91e5dd 100644
--- a/arch/powerpc/sysdev/bestcomm/ata.c
+++ b/arch/powerpc/sysdev/bestcomm/ata.c
@@ -61,6 +61,9 @@ bcom_ata_init(int queue_len, int maxbufsize)
         struct bcom_ata_var *var;
         struct bcom_ata_inc *inc;
 
+        /* Prefetch breaks ATA DMA.  Turn it off for ATA DMA */
+        bcom_disable_prefetch();
+
         tsk = bcom_task_alloc(queue_len, sizeof(struct bcom_ata_bd), 0);
         if (!tsk)
                 return NULL;
diff --git a/arch/powerpc/sysdev/bestcomm/bestcomm.c b/arch/powerpc/sysdev/bestcomm/bestcomm.c
index 446c9ea85b30..378ebd9aac18 100644
--- a/arch/powerpc/sysdev/bestcomm/bestcomm.c
+++ b/arch/powerpc/sysdev/bestcomm/bestcomm.c
@@ -279,7 +279,6 @@ bcom_engine_init(void)
         int task;
         phys_addr_t tdt_pa, ctx_pa, var_pa, fdt_pa;
         unsigned int tdt_size, ctx_size, var_size, fdt_size;
-        u16 regval;
 
         /* Allocate & clear SRAM zones for FDT, TDTs, contexts and vars/incs */
         tdt_size = BCOM_MAX_TASKS * sizeof(struct bcom_tdt);
@@ -331,10 +330,8 @@ bcom_engine_init(void)
         out_8(&bcom_eng->regs->ipr[BCOM_INITIATOR_ALWAYS], BCOM_IPR_ALWAYS);
 
         /* Disable COMM Bus Prefetch on the original 5200; it's broken */
-        if ((mfspr(SPRN_SVR) & MPC5200_SVR_MASK) == MPC5200_SVR) {
-                regval = in_be16(&bcom_eng->regs->PtdCntrl);
-                out_be16(&bcom_eng->regs->PtdCntrl,  regval | 1);
-        }
+        if ((mfspr(SPRN_SVR) & MPC5200_SVR_MASK) == MPC5200_SVR)
+                bcom_disable_prefetch();
 
         /* Init lock */
         spin_lock_init(&bcom_eng->lock);
diff --git a/arch/powerpc/sysdev/bestcomm/bestcomm_priv.h b/arch/powerpc/sysdev/bestcomm/bestcomm_priv.h
index 746f1551c8a5..eb0d1c883c31 100644
--- a/arch/powerpc/sysdev/bestcomm/bestcomm_priv.h
+++ b/arch/powerpc/sysdev/bestcomm/bestcomm_priv.h
@@ -241,6 +241,22 @@ extern void bcom_set_initiator(int task, int initiator);
 
 #define TASK_ENABLE             0x8000
 
+/**
+ * bcom_disable_prefetch - Hook to disable bus prefetching
+ *
+ * ATA DMA and the original MPC5200 need this due to silicon bugs.  At the
+ * moment disabling prefetch is a one-way street.  There is no mechanism
+ * in place to turn prefetch back on after it has been disabled.  There is
+ * no reason it couldn't be done, it would just be more complex to implement.
+ */
+static inline void bcom_disable_prefetch(void)
+{
+        u16 regval;
+
+        regval = in_be16(&bcom_eng->regs->PtdCntrl);
+        out_be16(&bcom_eng->regs->PtdCntrl, regval | 1);
+};
+
 static inline void
 bcom_enable_task(int task)
 {