fbtft: experimental DMA support

A DMA capable SPI master driver is needed to use DMA.

Tested-by: Derek Campbell

fbtft-core.c

@@ -36,6 +36,7 @@
 #include <linux/backlight.h>
 #include <linux/platform_device.h>
 #include <linux/spinlock.h>
+#include <linux/dma-mapping.h>
 
 #include "fbtft.h"
 
@@ -49,6 +50,10 @@ static unsigned long debug;
 module_param(debug, ulong , 0);
 MODULE_PARM_DESC(debug, "override device debug level");
 
+static bool dma;
+module_param(dma, bool, 0);
+MODULE_PARM_DESC(dma, "Use DMA buffer");
+
 
 void fbtft_dbg_hex(const struct device *dev, int groupsize,
 			void *buf, size_t len, const char *fmt, ...)
@@ -788,7 +793,12 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
 #endif
 
 	if (txbuflen > 0) {
-		txbuf = vzalloc(txbuflen);
+		if (dma) {
+			dev->coherent_dma_mask = ~0;
+			txbuf = dma_alloc_coherent(dev, txbuflen, &par->txbuf.dma, GFP_DMA);
+		} else {
+			txbuf = vzalloc(txbuflen);
+		}
 		if (!txbuf)
 			goto alloc_fail;
 		par->txbuf.buf = txbuf;
@@ -817,8 +827,6 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
 alloc_fail:
 	if (vmem)
 		vfree(vmem);
-	if (txbuf)
-		vfree(txbuf);
 	if (buf)
 		vfree(buf);
 	kfree(fbops);
@@ -841,8 +849,12 @@ void fbtft_framebuffer_release(struct fb_info *info)
 
 	fb_deferred_io_cleanup(info);
 	vfree(info->screen_base);
-	if (par->txbuf.buf)
-		vfree(par->txbuf.buf);
+	if (par->txbuf.buf) {
+		if (par->txbuf.dma)
+			dma_free_coherent(info->device, par->txbuf.len, par->txbuf.buf, par->txbuf.dma);
+		else
+			vfree(par->txbuf.buf);
+	}
 	vfree(par->buf);
 	kfree(info->fbops);
 	kfree(info->fbdefio);
@@ -921,7 +933,8 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
 	fbtft_sysfs_init(par);
 
 	if (par->txbuf.buf)
-		sprintf(text1, ", %d KiB buffer memory", par->txbuf.len >> 10);
+		sprintf(text1, ", %d KiB %sbuffer memory",
+			par->txbuf.len >> 10, par->txbuf.dma ? "DMA " : "");
 	if (spi)
 		sprintf(text2, ", spi%d.%d at %d MHz", spi->master->bus_num,
 				spi->chip_select, spi->max_speed_hz/1000000);

fbtft-io.c

@@ -9,6 +9,12 @@
 
 int fbtft_write_spi(struct fbtft_par *par, void *buf, size_t len)
 {
+	struct spi_transfer t = {
+		.tx_buf = buf,
+		.len = len,
+	};
+	struct spi_message m;
+
 	fbtft_par_dbg_hex(DEBUG_WRITE, par, par->info->device, u8, buf, len,
 		"%s(len=%d): ", __func__, len);
 
@@ -17,7 +23,14 @@ int fbtft_write_spi(struct fbtft_par *par, void *buf, size_t len)
 			"%s: par->spi is unexpectedly NULL\n", __func__);
 		return -1;
 	}
-	return spi_write(par->spi, buf, len);
+
+	spi_message_init(&m);
+	if (par->txbuf.dma && buf == par->txbuf.buf) {
+		t.tx_dma = par->txbuf.dma;
+		m.is_dma_mapped = 1;
+	}
+	spi_message_add_tail(&t, &m);
+	return spi_sync(par->spi, &m);
 }
 EXPORT_SYMBOL(fbtft_write_spi);
 

fbtft.h

@@ -219,6 +219,7 @@ struct fbtft_par {
 	u32 pseudo_palette[16];
 	struct {
 		void *buf;
+		dma_addr_t dma;
 		size_t len;
 	} txbuf;
 	u8 *buf;