Re: [PATCH v2 2/2] drm/tinydrm: Remove chunk splitting in tinydrm_spi_transfer

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Den 10.03.2018 16.52, skrev Meghana Madhyastha:
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.

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@xxxxxxxxx>
---
  drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c | 48 ++++----------------------
  drivers/gpu/drm/tinydrm/mipi-dbi.c             | 10 ++----
  drivers/spi/spi-bcm2835.c                      |  2 +-
  3 files changed, 9 insertions(+), 51 deletions(-)

diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
index bf96072d1b97..6064099e8e63 100644
--- a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
+++ b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
@@ -452,62 +452,26 @@ 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);
+	max_chunk = SIZE_MAX;

max_chunk isn't used so can be removed.
tinydrm_spi_max_transfer_size() can also be remove now.

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;
-		}
-	}
+			__func__, bpw, max_chunk);
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);
-
-		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;
-	}
+	tinydrm_dbg_spi_message(spi, &m);
- 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 75dd65c57e74..c8af2d65c2ad 100644
--- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
+++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
@@ -886,15 +886,9 @@ 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
@@ -924,8 +918,8 @@ 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;
  	}
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index 0dcc45f158b8..2fd650891c07 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -448,7 +448,7 @@ static void bcm2835_dma_init(struct spi_master *master, struct device *dev)
/* all went well, so set can_dma */
  	master->can_dma = bcm2835_spi_can_dma;
-	master->max_dma_len = 65535; /* limitation by BCM2835_SPI_DLEN */
+	master->max_dma_len = 65528; /* limitation by BCM2835_SPI_DLEN */

This change belongs in the spi-bcm2835 patch.
You need to tell us why the change is needed.

Noralf.

  	/* need to do TX AND RX DMA, so we need dummy buffers */
  	master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;

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