staging: fbtft: remove custom DMA mapped buffer

There is no need to duplicate what SPI core already does, i.e. mapping buffers
for DMA capable transfers.

Remove all related pices of code.

Note, that code, besides its redundancy, was buggy: DMA address potentially can
be 0, SPI slave device has nothing to do with DMA capable device properties and
DMA mask in particular.

Suggested-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fb_ra8875.c

@@ -42,10 +42,6 @@ static int write_spi(struct fbtft_par *par, void *buf, size_t 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);
 }

drivers/staging/fbtft/fbtft-core.c

@@ -32,7 +32,6 @@
 #include <linux/backlight.h>
 #include <linux/platform_device.h>
 #include <linux/spinlock.h>
-#include <linux/dma-mapping.h>
 #include <linux/of.h>
 #include <linux/of_gpio.h>
 #include <video/mipi_display.h>
@@ -44,12 +43,6 @@ static unsigned long debug;
 module_param(debug, ulong, 0);
 MODULE_PARM_DESC(debug, "override device debug level");
 
-#ifdef CONFIG_HAS_DMA
-static bool dma = true;
-module_param(dma, bool, 0);
-MODULE_PARM_DESC(dma, "Use DMA buffer");
-#endif
-
 void fbtft_dbg_hex(const struct device *dev, int groupsize,
 			void *buf, size_t len, const char *fmt, ...)
 {
@@ -836,17 +829,7 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
 #endif
 
 	if (txbuflen > 0) {
-#ifdef CONFIG_HAS_DMA
-		if (dma) {
-			dev->coherent_dma_mask = ~0;
-			txbuf = dmam_alloc_coherent(dev, txbuflen,
-						    &par->txbuf.dma, GFP_DMA);
-		} else
-#endif
-		{
-			txbuf = devm_kzalloc(par->info->device,
-					     txbuflen, GFP_KERNEL);
-		}
+		txbuf = devm_kzalloc(par->info->device, txbuflen, GFP_KERNEL);
 		if (!txbuf)
 			goto alloc_fail;
 		par->txbuf.buf = txbuf;
@@ -975,8 +958,7 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
 	fbtft_sysfs_init(par);
 
 	if (par->txbuf.buf)
-		sprintf(text1, ", %zu KiB %sbuffer memory",
-			par->txbuf.len >> 10, par->txbuf.dma ? "DMA " : "");
+		sprintf(text1, ", %zu KiB buffer memory", par->txbuf.len >> 10);
 	if (spi)
 		sprintf(text2, ", spi%d.%d at %d MHz", spi->master->bus_num,
 			spi->chip_select, spi->max_speed_hz / 1000000);

drivers/staging/fbtft/fbtft-io.c

@@ -22,10 +22,6 @@ int fbtft_write_spi(struct fbtft_par *par, void *buf, size_t 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);
 }

drivers/staging/fbtft/fbtft.h

@@ -209,7 +209,6 @@ struct fbtft_par {
 	u32 pseudo_palette[16];
 	struct {
 		void *buf;
-		dma_addr_t dma;
 		size_t len;
 	} txbuf;
 	u8 *buf;