[U-Boot] [PATCH 4/4] spi: sh_qspi: Make use of the 32byte FIFO

[Marek Vasut]

The QSPI controller on RCar Gen2 has 32byte FIFO. Instead of doing
the SPI transmission 1 byte at time, if there is a 32byte chunk of
data to be transferred, fill the FIFO completely and then transfer
the data to/from the FIFO. This increases the SPI NOR access speed
significantly.

Signed-off-by: Marek Vasut <marek.vasut+rene...@gmail.com>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu...@renesas.com>
---
 drivers/spi/sh_qspi.c | 34 ++++++++++++++++++++++++----------
 1 file changed, 24 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/sh_qspi.c b/drivers/spi/sh_qspi.c
index d7f558a541..5075be3cd1 100644
--- a/drivers/spi/sh_qspi.c
+++ b/drivers/spi/sh_qspi.c
@@ -36,6 +36,8 @@
                        SPCMD_BRDV0
 #define SPBFCR_TXRST   BIT(7)
 #define SPBFCR_RXRST   BIT(6)
+#define SPBFCR_TXTRG   0x30
+#define SPBFCR_RXTRG   0x07
 
 /* SH QSPI register set */
 struct sh_qspi_regs {
@@ -201,8 +203,8 @@ int spi_xfer(struct spi_slave *slave, unsigned int bitlen, 
const void *dout,
             void *din, unsigned long flags)
 {
        struct sh_qspi_slave *ss = to_sh_qspi(slave);
-       u32 nbyte;
-       int ret = 0;
+       u32 nbyte, chunk;
+       int i, ret = 0;
        u8 dtdata = 0, drdata;
        u8 *tdata = &dtdata, *rdata = &drdata;
        u32 *spbmul0 = &ss->regs->spbmul0;
@@ -237,26 +239,38 @@ int spi_xfer(struct spi_slave *slave, unsigned int 
bitlen, const void *dout,
                rdata = din;
 
        while (nbyte > 0) {
+               /*
+                * Check if there is 32 Byte chunk and if there is, transfer
+                * it in one burst, otherwise transfer on byte-by-byte basis.
+                */
+               chunk = (nbyte >= 32) ? 32 : 1;
+
+               clrsetbits_8(&ss->regs->spbfcr, SPBFCR_TXTRG | SPBFCR_RXTRG,
+                            chunk == 32 ? SPBFCR_TXTRG | SPBFCR_RXTRG : 0);
+
                ret = wait_for_bit_8(&ss->regs->spsr, SPSR_SPTEF,
                                     true, 1000, true);
                if (ret)
                        return ret;
 
-               writeb(*tdata, (u8 *)(&ss->regs->spdr));
+               for (i = 0; i < chunk; i++) {
+                       writeb(*tdata, &ss->regs->spdr);
+                       if (dout != NULL)
+                               tdata++;
+               }
 
                ret = wait_for_bit_8(&ss->regs->spsr, SPSR_SPRFF,
                                     true, 1000, true);
                if (ret)
                        return ret;
 
-               *rdata = readb((u8 *)(&ss->regs->spdr));
-
-               if (dout != NULL)
-                       tdata++;
-               if (din != NULL)
-                       rdata++;
+               for (i = 0; i < chunk; i++) {
+                       *rdata = readb(&ss->regs->spdr);
+                       if (din != NULL)
+                               rdata++;
+               }
 
-               nbyte--;
+               nbyte -= chunk;
        }
 
        if (flags & SPI_XFER_END)
-- 
2.16.2

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