[PATCH] Nvidia MCP SPI speedup

[Carl-Daniel Hailfinger]

Use caching for Nvidia MCP SPI GPIO accesses.
Reduce clock delay to zero.

Should result in a 2x speedup, maybe more.

Signed-off-by: Carl-Daniel Hailfinger

Index: flashrom-bitbang_spi_nvidia_mcp_faster/mcp6x_spi.c
===================================================================
--- flashrom-bitbang_spi_nvidia_mcp_faster/mcp6x_spi.c	(Revision 1130)
+++ flashrom-bitbang_spi_nvidia_mcp_faster/mcp6x_spi.c	(Arbeitskopie)
@@ -42,41 +42,39 @@

void *mcp6x_spibar = NULL;

+/* Cached value of last GPIO state. */
+static uint8_t mcp_gpiostate;
+
 static void mcp6x_request_spibus(void)
 {
-	uint8_t tmp;
+	mcp_gpiostate = mmio_readb(mcp6x_spibar + 0x530);
+	mcp_gpiostate |= 1 << MCP6X_SPI_REQUEST;
+	mmio_writeb(mcp_gpiostate, mcp6x_spibar + 0x530);

-	tmp = mmio_readb(mcp6x_spibar + 0x530);
-	tmp |= 1 << MCP6X_SPI_REQUEST;
-	mmio_writeb(tmp, mcp6x_spibar + 0x530);
-
    /* Wait until we are allowed to use the SPI bus. */
    while (!(mmio_readw(mcp6x_spibar + 0x530) & (1 << MCP6X_SPI_GRANT))) ;
+
+	/* Update the cache. */
+	mcp_gpiostate = mmio_readb(mcp6x_spibar + 0x530);
 }

static void mcp6x_release_spibus(void)
 {
-	uint8_t tmp;
-
-	tmp = mmio_readb(mcp6x_spibar + 0x530);
-	tmp &= ~(1 << MCP6X_SPI_REQUEST);
-	mmio_writeb(tmp, mcp6x_spibar + 0x530);
+	mcp_gpiostate &= ~(1 << MCP6X_SPI_REQUEST);
+	mmio_writeb(mcp_gpiostate, mcp6x_spibar + 0x530);
 }

static void mcp6x_bitbang_set_cs(int val)
 {
-	uint8_t tmp;
-
    /* Requesting and releasing the SPI bus is handled in here to allow the
     * chipset to use its own SPI engine for native reads.
     */
    if (val == 0)
    	mcp6x_request_spibus();

-	tmp = mmio_readb(mcp6x_spibar + 0x530);
-	tmp &= ~(1 << MCP6X_SPI_CS);
-	tmp |= (val << MCP6X_SPI_CS);
-	mmio_writeb(tmp, mcp6x_spibar + 0x530);
+	mcp_gpiostate &= ~(1 << MCP6X_SPI_CS);
+	mcp_gpiostate |= (val << MCP6X_SPI_CS);
+	mmio_writeb(mcp_gpiostate, mcp6x_spibar + 0x530);

if (val == 1)
    	mcp6x_release_spibus();
@@ -84,31 +82,22 @@

static void mcp6x_bitbang_set_sck(int val)
 {
-	uint8_t tmp;
-
-	tmp = mmio_readb(mcp6x_spibar + 0x530);
-	tmp &= ~(1 << MCP6X_SPI_SCK);
-	tmp |= (val << MCP6X_SPI_SCK);
-	mmio_writeb(tmp, mcp6x_spibar + 0x530);
+	mcp_gpiostate &= ~(1 << MCP6X_SPI_SCK);
+	mcp_gpiostate |= (val << MCP6X_SPI_SCK);
+	mmio_writeb(mcp_gpiostate, mcp6x_spibar + 0x530);
 }

static void mcp6x_bitbang_set_mosi(int val)
 {
-	uint8_t tmp;
-
-	tmp = mmio_readb(mcp6x_spibar + 0x530);
-	tmp &= ~(1 << MCP6X_SPI_MOSI);
-	tmp |= (val << MCP6X_SPI_MOSI);
-	mmio_writeb(tmp, mcp6x_spibar + 0x530);
+	mcp_gpiostate &= ~(1 << MCP6X_SPI_MOSI);
+	mcp_gpiostate |= (val << MCP6X_SPI_MOSI);
+	mmio_writeb(mcp_gpiostate, mcp6x_spibar + 0x530);
 }

static int mcp6x_bitbang_get_miso(void)
 {
-	uint8_t tmp;
-
-	tmp = mmio_readb(mcp6x_spibar + 0x530);
-	tmp = (tmp >> MCP6X_SPI_MISO) & 0x1;
-	return tmp;
+	mcp_gpiostate = mmio_readb(mcp6x_spibar + 0x530);
+	return (mcp_gpiostate >> MCP6X_SPI_MISO) & 0x1;
 }

static const struct bitbang_spi_master bitbang_spi_master_mcp6x = {
@@ -176,9 +165,10 @@
    msg_pdbg("SPI control is 0x%04x, req=%i, gnt=%i\n",
    	 status, (status >> MCP6X_SPI_REQUEST) & 0x1,
    	 (status >> MCP6X_SPI_GRANT) & 0x1);
+	mcp_gpiostate = status & 0xff;

-	/* 1 usec halfperiod delay for now. */
-	if (bitbang_spi_init(&bitbang_spi_master_mcp6x, 1)) {
+	/* Zero halfperiod delay. */
+	if (bitbang_spi_init(&bitbang_spi_master_mcp6x, 0)) {
    	/* This should never happen. */
    	msg_perr("MCP6X bitbang SPI master init failed!\n");
    	return 1;