[PATCH v2 05/10] hw/ssi: npcm7xx_fiu: Correct the dummy cycle emulation logic

[Bin Meng]

Change send_dummy_bits() to send_dummy_bytes() as the FIU register
fields are programmed from spi_mem_op.dummy.nbytes, so they already
describe byte transfers.

Verified the changes by booting OpenBMC image on `gbs` machine all
the way to the Linux login shell:

$ qemu-system-arm -machine quanta-gbs-bmc -nographic \
      -drive file=image.mtd,if=mtd,bus=0,unit=0,format=raw

Fixes: b821242c7b3b ("hw/ssi: NPCM7xx Flash Interface Unit device model")
Signed-off-by: Bin Meng <bin.m...@processmission.com>
---

(no changes since v1)

 hw/ssi/npcm7xx_fiu.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/hw/ssi/npcm7xx_fiu.c b/hw/ssi/npcm7xx_fiu.c
index 2d5bed005a..d41d877cfb 100644
--- a/hw/ssi/npcm7xx_fiu.c
+++ b/hw/ssi/npcm7xx_fiu.c
@@ -150,7 +150,7 @@ static uint64_t npcm7xx_fiu_flash_read(void *opaque, hwaddr 
addr,
     NPCM7xxFIUState *fiu = f->fiu;
     uint64_t value = 0;
     uint32_t drd_cfg;
-    int dummy_cycles;
+    int dummy_bytes;
     int i;
 
     if (fiu->active_cs != -1) {
@@ -180,10 +180,8 @@ static uint64_t npcm7xx_fiu_flash_read(void *opaque, 
hwaddr addr,
         break;
     }
 
-    /* Flash chip model expects one transfer per dummy bit, not byte */
-    dummy_cycles =
-        (FIU_DRD_CFG_DBW(drd_cfg) * 8) >> FIU_DRD_CFG_ACCTYPE(drd_cfg);
-    for (i = 0; i < dummy_cycles; i++) {
+    dummy_bytes = FIU_DRD_CFG_DBW(drd_cfg);
+    for (i = 0; i < dummy_bytes; i++) {
         ssi_transfer(fiu->spi, 0);
     }
 
@@ -305,20 +303,13 @@ static void send_address(SSIBus *spi, unsigned int 
addsiz, uint32_t addr)
     }
 }
 
-/* Send the number of dummy bits specified in the UMA config register. */
-static void send_dummy_bits(SSIBus *spi, uint32_t uma_cfg, uint32_t uma_cmd)
+/* Send the number of dummy bytes specified in the UMA config register */
+static void send_dummy_bytes(SSIBus *spi, uint32_t uma_cfg)
 {
-    unsigned int bits_per_clock = 1U << FIU_UMA_CFG_DBPCK(uma_cfg);
     unsigned int i;
 
     for (i = 0; i < FIU_UMA_CFG_DBSIZ(uma_cfg); i++) {
-        /* Use bytes 0 and 1 first, then keep repeating byte 2 */
-        unsigned int field = (i < 2) ? ((i + 1) * 8) : 24;
-        unsigned int j;
-
-        for (j = 0; j < 8; j += bits_per_clock) {
-            ssi_transfer(spi, extract32(uma_cmd, field + j, bits_per_clock));
-        }
+        ssi_transfer(spi, 0);
     }
 }
 
@@ -354,8 +345,8 @@ static void npcm7xx_fiu_uma_transaction(NPCM7xxFIUState *s)
         ssi_transfer(s->spi, extract32(s->regs[reg], field, 8));
     }
 
-    /* Send dummy bits, if present. */
-    send_dummy_bits(s->spi, uma_cfg, s->regs[NPCM7XX_FIU_UMA_CMD]);
+    /* Send dummy bytes, if present */
+    send_dummy_bytes(s->spi, uma_cfg);
 
     /* Read data, if present. */
     for (i = 0; i < FIU_UMA_CFG_RDATSIZ(uma_cfg); i++) {
-- 
2.53.0