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

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

[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.
-Remove automatic byte swapping in tinydrm_spi_transfer as it doesn't have users.
-Remove the upper bound check on dma transfer length in bcm2835_spi_can_dma().

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@gmail.com>
---
 drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c | 48 ++++----------------------
 drivers/gpu/drm/tinydrm/mipi-dbi.c             | 10 ++----
 drivers/spi/spi-bcm2835.c                      | 15 +-------
 3 files changed, 9 insertions(+), 64 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;
 
 	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 f35cc10772f6..2fd650891c07 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -365,19 +365,6 @@ static bool bcm2835_spi_can_dma(struct spi_master *master,
 	if (tfr->len < BCM2835_SPI_DMA_MIN_LENGTH)
 		return false;
 
-	/* BCM2835_SPI_DLEN has defined a max transfer size as
-	 * 16 bit, so max is 65535
-	 * we can revisit this by using an alternative transfer
-	 * method - ideally this would get done without any more
-	 * interaction...
-	 */
-	if (tfr->len > 65535) {
-		dev_warn_once(&spi->dev,
-			      "transfer size of %d too big for dma-transfer\n",
-			      tfr->len);
-		return false;
-	}
-
 	/* if we run rx/tx_buf with word aligned addresses then we are OK */
 	if ((((size_t)tfr->rx_buf & 3) == 0) &&
 	    (((size_t)tfr->tx_buf & 3) == 0))
@@ -461,7 +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 */
 	/* need to do TX AND RX DMA, so we need dummy buffers */
 	master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;
 
-- 
2.11.0

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

[Mark Brown]

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On Mon, Feb 19, 2018 at 11:47:23AM +0000, Meghana Madhyastha wrote:
> -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.
> -Remove automatic byte swapping in tinydrm_spi_transfer as it doesn't have users.
> -Remove the upper bound check on dma transfer length in bcm2835_spi_can_dma().

This looks like a series of related changes that should be split up into
individual commits, probably at least one per bullet point there.

> -	/* BCM2835_SPI_DLEN has defined a max transfer size as
> -	 * 16 bit, so max is 65535
> -	 * we can revisit this by using an alternative transfer
> -	 * method - ideally this would get done without any more
> -	 * interaction...
> -	 */
> -	if (tfr->len > 65535) {
> -		dev_warn_once(&spi->dev,
> -			      "transfer size of %d too big for dma-transfer\n",
> -			      tfr->len);
> -		return false;
> -	}
> -

The changelog says we're removing this check but doesn't explain why
and...

>  	/* if we run rx/tx_buf with word aligned addresses then we are OK */
>  	if ((((size_t)tfr->rx_buf & 3) == 0) &&
>  	    (((size_t)tfr->tx_buf & 3) == 0))
> @@ -461,7 +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 */
>  	/* need to do TX AND RX DMA, so we need dummy buffers */
>  	master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;

...this bit of the change isn't mentioned at all?

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