ucmb: Allow chunk-ing big transfers to reduce latency issues.

SVN-Revision: 14839

diff --git a/utils/ucmb/driver/ucmb.c b/utils/ucmb/driver/ucmb.c
index 374f467212317cc64214e99d6e285efb53e56b1c..bd02d9e8aadfdc4d5960f58d65c937690ca8bc25 100644 (file)
--- a/utils/ucmb/driver/ucmb.c
+++ b/utils/ucmb/driver/ucmb.c
@@ -28,6 +28,7 @@
 #include <linux/gfp.h>
 #include <linux/delay.h>
 #include <linux/crc16.h>
+#include <linux/sched.h>
 
 #include <asm/uaccess.h>
 
@@ -47,6 +48,7 @@ struct ucmb {
 
        bool is_open;
 
+       unsigned int chunk_size;
        unsigned int msg_delay_usec;
        unsigned int gpio_reset;
        bool reset_activelow;
@@ -228,6 +230,48 @@ static int ucmb_ioctl(struct inode *inode, struct file *filp,
        return ret;
 }
 
+static int ucmb_spi_write(struct ucmb *ucmb, const void *_buf, size_t size)
+{
+       const u8 *buf = _buf;
+       size_t i, chunk_size, current_size;
+       int err = 0;
+
+       chunk_size = ucmb->chunk_size ? : size;
+       for (i = 0; i < size; i += chunk_size) {
+               current_size = chunk_size;
+               if (i + current_size > size)
+                       current_size = size - i;
+               err = spi_write(ucmb->sdev, buf + i, current_size);
+               if (err)
+                       goto out;
+               if (ucmb->chunk_size && need_resched())
+                       msleep(1);
+       }
+out:
+       return err;
+}
+
+static int ucmb_spi_read(struct ucmb *ucmb, void *_buf, size_t size)
+{
+       u8 *buf = _buf;
+       size_t i, chunk_size, current_size;
+       int err = 0;
+
+       chunk_size = ucmb->chunk_size ? : size;
+       for (i = 0; i < size; i += chunk_size) {
+               current_size = chunk_size;
+               if (i + current_size > size)
+                       current_size = size - i;
+               err = spi_read(ucmb->sdev, buf + i, current_size);
+               if (err)
+                       goto out;
+               if (ucmb->chunk_size && need_resched())
+                       msleep(1);
+       }
+out:
+       return err;
+}
+
 static ssize_t ucmb_read(struct file *filp, char __user *user_buf,
                         size_t size, loff_t *offp)
 {
@@ -248,7 +292,7 @@ static ssize_t ucmb_read(struct file *filp, char __user *user_buf,
        if (!buf)
                goto out;
 
-       err = spi_read(ucmb->sdev, (u8 *)&hdr, sizeof(hdr));
+       err = ucmb_spi_read(ucmb, &hdr, sizeof(hdr));
        if (err)
                goto out_free;
 #ifdef DEBUG
@@ -262,10 +306,10 @@ static ssize_t ucmb_read(struct file *filp, char __user *user_buf,
        if (size < le16_to_cpu(hdr.len))
                goto out_free;
        size = le16_to_cpu(hdr.len);
-       err = spi_read(ucmb->sdev, buf, size);
+       err = ucmb_spi_read(ucmb, buf, size);
        if (err)
                goto out_free;
-       err = spi_read(ucmb->sdev, (u8 *)&footer, sizeof(footer));
+       err = ucmb_spi_read(ucmb, &footer, sizeof(footer));
        if (err)
                goto out_free;
 
@@ -288,7 +332,7 @@ static ssize_t ucmb_read(struct file *filp, char __user *user_buf,
        err = 0;
 
 out_send_status:
-       res = spi_write(ucmb->sdev, (u8 *)&status, sizeof(status));
+       res = ucmb_spi_write(ucmb, &status, sizeof(status));
        if (res && !err)
                err = res;
 out_free:
@@ -308,10 +352,7 @@ static ssize_t ucmb_write(struct file *filp, const char __user *user_buf,
        struct ucmb_message_hdr hdr = { .magic = cpu_to_le16(UCMB_MAGIC), };
        struct ucmb_message_footer footer = { .crc = 0xFFFF, };
        struct ucmb_status status;
-       struct spi_transfer spi_hdr_xfer;
-       struct spi_transfer spi_footer_xfer;
-       struct spi_transfer spi_data_xfer;
-       struct spi_message spi_msg;
+       size_t i, current_size, chunk_size;
 
        mutex_lock(&ucmb->mutex);
 
@@ -330,25 +371,13 @@ static ssize_t ucmb_write(struct file *filp, const char __user *user_buf,
        footer.crc = crc16(footer.crc, buf, size);
        footer.crc ^= 0xFFFF;
 
-       spi_message_init(&spi_msg);
-
-       memset(&spi_hdr_xfer, 0, sizeof(spi_hdr_xfer));
-       spi_hdr_xfer.tx_buf = &hdr;
-       spi_hdr_xfer.len = sizeof(hdr);
-       spi_message_add_tail(&spi_hdr_xfer, &spi_msg);
-
-       memset(&spi_data_xfer, 0, sizeof(spi_data_xfer));
-       spi_data_xfer.tx_buf = buf;
-       spi_data_xfer.len = size;
-       spi_message_add_tail(&spi_data_xfer, &spi_msg);
-
-       memset(&spi_footer_xfer, 0, sizeof(spi_footer_xfer));
-       spi_footer_xfer.tx_buf = &footer;
-       spi_footer_xfer.len = sizeof(footer);
-       spi_message_add_tail(&spi_footer_xfer, &spi_msg);
-
-       /* Send the message, including header. */
-       err = spi_sync(ucmb->sdev, &spi_msg);
+       err = ucmb_spi_write(ucmb, &hdr, sizeof(hdr));
+       if (err)
+               goto out_free;
+       err = ucmb_spi_write(ucmb, buf, size);
+       if (err)
+               goto out_free;
+       err = ucmb_spi_write(ucmb, &footer, sizeof(footer));
        if (err)
                goto out_free;
 
@@ -364,7 +393,7 @@ static ssize_t ucmb_write(struct file *filp, const char __user *user_buf,
        }
 
        /* Get the status code. */
-       err = spi_read(ucmb->sdev, (u8 *)&status, sizeof(status));
+       err = ucmb_spi_read(ucmb, &status, sizeof(status));
        if (err)
                goto out_free;
 #ifdef DEBUG
@@ -404,6 +433,14 @@ static int __devinit ucmb_probe(struct platform_device *pdev)
        mutex_init(&ucmb->mutex);
        ucmb->gpio_reset = pdata->gpio_reset;
        ucmb->reset_activelow = pdata->reset_activelow;
+       ucmb->chunk_size = pdata->chunk_size;
+
+#ifdef CONFIG_PREEMPT
+       /* A preemptible kernel does not need to sleep between
+        * chunks, because it can sleep at desire (if IRQs are enabled).
+        * So transmit/receive it all in one go. */
+       ucmb->chunk_size = 0;
+#endif
 
        /* Create the SPI GPIO bus master. */
 

diff --git a/utils/ucmb/driver/ucmb.h b/utils/ucmb/driver/ucmb.h
index d64f2e4f66f65103628c134f21ad830a14fb9e4a..c0d35d20733d068f4cf12c9512b3bbfb2c5c4cc6 100644 (file)
--- a/utils/ucmb/driver/ucmb.h
+++ b/utils/ucmb/driver/ucmb.h
@@ -41,6 +41,13 @@
  *
  * @mode:              The SPI bus mode. SPI_MODE_*
  * @max_speed_hz:      The bus speed, in Hz. If zero the speed is not limited.
+ * @chunk_size:                The maximum chunk size to transmit/receive in one go
+ *                     without sleeping. The kernel will be allowed to sleep
+ *                     after each chunk.
+ *                     If set to 0, the whole data will be transmitted/received
+ *                     in one big rush without sleeping. Note that this might hurt
+ *                     system responsiveness, if the kernel is not preemptible.
+ *                     If CONFIG_PREEMPT is enabled, chunk_size will be forced to 0.
  */
 struct ucmb_platform_data {
        const char *name;
@@ -55,6 +62,7 @@ struct ucmb_platform_data {
 
        u8 mode;
        u32 max_speed_hz;
+       unsigned int chunk_size;
 
        struct platform_device *pdev; /* internal */
 };