[PATCH v4 4/4] drm/tinydrm: Remove chunk splitting in tinydrm_spi_transfer

[Noralf Trønnes <noralf@xxxxxxxxxxx>]

From: Meghana Madhyastha <meghana.madhyastha@xxxxxxxxx>

Remove chunk splitting in tinydrm_spi_transfer in tinydrm-helpers as the
spi core will split a buffer into max_dma_len chunks for the spi
controller driver to handle, automatic byte swapping in
tinydrm_spi_transfer as it doesn't have users.

Remove the spi_max module argument that now has lost its cause.

The 16kB buffer size for Type C Option 1 (9-bit) interface is somewhat
arbitrary, but a bigger buffer will have a miniscule impact on transfer
speed, so it's probably fine.

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@xxxxxxxxx>
Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
---
 .../gpu/drm/tinydrm/core/tinydrm-helpers.c    | 83 ++-----------------
 drivers/gpu/drm/tinydrm/mipi-dbi.c            | 10 +--
 2 files changed, 7 insertions(+), 86 deletions(-)

diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
index 6d540d93758f..a32dc859a9c1 100644
--- a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
+++ b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
@@ -22,41 +22,8 @@
 #include <drm/drm_rect.h>
 #include <drm/tinydrm/tinydrm-helpers.h>
 
-static unsigned int spi_max;
-module_param(spi_max, uint, 0400);
-MODULE_PARM_DESC(spi_max, "Set a lower SPI max transfer size");
-
 #if IS_ENABLED(CONFIG_SPI)
 
-/**
- * tinydrm_spi_max_transfer_size - Determine max SPI transfer size
- * @spi: SPI device
- * @max_len: Maximum buffer size needed (optional)
- *
- * This function returns the maximum size to use for SPI transfers. It checks
- * the SPI master, the optional @max_len and the module parameter spi_max and
- * returns the smallest.
- *
- * Returns:
- * Maximum size for SPI transfers
- */
-size_t tinydrm_spi_max_transfer_size(struct spi_device *spi, size_t max_len)
-{
-	size_t ret;
-
-	ret = min(spi_max_transfer_size(spi), spi->master->max_dma_len);
-	if (max_len)
-		ret = min(ret, max_len);
-	if (spi_max)
-		ret = min_t(size_t, ret, spi_max);
-	ret &= ~0x3;
-	if (ret < 4)
-		ret = 4;
-
-	return ret;
-}
-EXPORT_SYMBOL(tinydrm_spi_max_transfer_size);
-
 /**
  * tinydrm_spi_bpw_supported - Check if bits per word is supported
  * @spi: SPI device
@@ -147,62 +114,22 @@ int tinydrm_spi_transfer(struct spi_device *spi, u32 speed_hz,
 	struct spi_transfer tr = {
 		.bits_per_word = bpw,
 		.speed_hz = speed_hz,
+		.tx_buf = buf,
+		.len = len
 	};
 	struct spi_message m;
-	u16 *swap_buf = NULL;
-	size_t max_chunk;
-	size_t chunk;
-	int ret = 0;
-
-	if (WARN_ON_ONCE(bpw != 8 && bpw != 16))
-		return -EINVAL;
-
-	max_chunk = tinydrm_spi_max_transfer_size(spi, 0);
 
 	if (drm_debug & DRM_UT_DRIVER)
-		pr_debug("[drm:%s] bpw=%u, max_chunk=%zu, transfers:\n",
-			 __func__, bpw, max_chunk);
-
-	if (bpw == 16 && !tinydrm_spi_bpw_supported(spi, 16)) {
-		tr.bits_per_word = 8;
-		if (tinydrm_machine_little_endian()) {
-			swap_buf = kmalloc(min(len, max_chunk), GFP_KERNEL);
-			if (!swap_buf)
-				return -ENOMEM;
-		}
-	}
+		pr_debug("[drm:%s] bpw=%u, transfers:\n", __func__, bpw);
 
 	spi_message_init(&m);
 	if (header)
 		spi_message_add_tail(header, &m);
 	spi_message_add_tail(&tr, &m);
 
-	while (len) {
-		chunk = min(len, max_chunk);
+	tinydrm_dbg_spi_message(spi, &m);
 
-		tr.tx_buf = buf;
-		tr.len = chunk;
-
-		if (swap_buf) {
-			const u16 *buf16 = buf;
-			unsigned int i;
-
-			for (i = 0; i < chunk / 2; i++)
-				swap_buf[i] = swab16(buf16[i]);
-
-			tr.tx_buf = swap_buf;
-		}
-
-		buf += chunk;
-		len -= chunk;
-
-		tinydrm_dbg_spi_message(spi, &m);
-		ret = spi_sync(spi, &m);
-		if (ret)
-			return ret;
-	}
-
-	return 0;
+	return spi_sync(spi, &m);
 }
 EXPORT_SYMBOL(tinydrm_spi_transfer);
 
diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c b/drivers/gpu/drm/tinydrm/mipi-dbi.c
index 85761b4abb83..0bcf6c764893 100644
--- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
+++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
@@ -975,15 +975,9 @@ static int mipi_dbi_typec3_command(struct mipi_dbi *mipi, u8 *cmd,
 int mipi_dbi_spi_init(struct spi_device *spi, struct mipi_dbi *mipi,
 		      struct gpio_desc *dc)
 {
-	size_t tx_size = tinydrm_spi_max_transfer_size(spi, 0);
 	struct device *dev = &spi->dev;
 	int ret;
 
-	if (tx_size < 16) {
-		DRM_ERROR("SPI transmit buffer too small: %zu\n", tx_size);
-		return -EINVAL;
-	}
-
 	/*
 	 * Even though it's not the SPI device that does DMA (the master does),
 	 * the dma mask is necessary for the dma_alloc_wc() in
@@ -1013,8 +1007,8 @@ int mipi_dbi_spi_init(struct spi_device *spi, struct mipi_dbi *mipi,
 			mipi->swap_bytes = true;
 	} else {
 		mipi->command = mipi_dbi_typec1_command;
-		mipi->tx_buf9_len = tx_size;
-		mipi->tx_buf9 = devm_kmalloc(dev, tx_size, GFP_KERNEL);
+		mipi->tx_buf9_len = SZ_16K;
+		mipi->tx_buf9 = devm_kmalloc(dev, mipi->tx_buf9_len, GFP_KERNEL);
 		if (!mipi->tx_buf9)
 			return -ENOMEM;
 	}
-- 
2.20.1