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Subject[PATCH 6/7] mmc_spi: convert timeout handling to jiffies and avoid busy waiting
Date
From: Wolfgang Muees <wolfgang.mues@auerswald.de>

o SD/MMC card timeouts can be very high. So avoid busy-waiting,
using the scheduler. Calculate all timeouts in jiffies units,
because this will give us the correct sign when to involve
the scheduler.

Signed-off-by: Wolfgang Muees <wolfgang.mues@auerswald.de>

---
This is one of a line of patches to enhance the usability of
the mmc spi host port driver from "don't work with most SD cards"
to "work with nearly all SD cards" (including those ugly cards
with non-byte-aligned responses).

diff -uprN 2_6_29_rc7_patch5_extra_spi_timeouts/drivers/mmc/host/mmc_spi.c 2_6_29_rc7_patch6_jiffies_and_scheduling/drivers/mmc/host/mmc_spi.c
--- 2_6_29_rc7_patch5_extra_spi_timeouts/drivers/mmc/host/mmc_spi.c 2009-03-11 13:43:39.000000000 +0100
+++ 2_6_29_rc7_patch6_jiffies_and_scheduling/drivers/mmc/host/mmc_spi.c 2009-03-11 13:49:53.000000000 +0100
@@ -24,7 +24,7 @@
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
-#include <linux/hrtimer.h>
+#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/bio.h>
#include <linux/dma-mapping.h>
@@ -95,7 +95,7 @@
* reads which takes nowhere near that long. Older cards may be able to use
* shorter timeouts ... but why bother?
*/
-#define r1b_timeout ktime_set(3, 0)
+#define r1b_timeout (HZ * 3)


/****************************************************************************/
@@ -183,12 +183,11 @@ mmc_spi_readbytes(struct mmc_spi_host *h
return status;
}

-static int
-mmc_spi_skip(struct mmc_spi_host *host, ktime_t timeout, unsigned n, u8 byte)
+static int mmc_spi_skip(struct mmc_spi_host *host, unsigned long timeout,
+ unsigned n, u8 byte)
{
u8 *cp = host->data->status;
-
- timeout = ktime_add(timeout, ktime_get());
+ unsigned long start = jiffies;

while (1) {
int status;
@@ -203,22 +202,26 @@ mmc_spi_skip(struct mmc_spi_host *host,
return cp[i];
}

- /* REVISIT investigate msleep() to avoid busy-wait I/O
- * in at least some cases.
- */
- if (ktime_to_ns(ktime_sub(ktime_get(), timeout)) > 0)
+ if (time_is_before_jiffies(start + timeout))
break;
+
+ /* If we need long timeouts, we may release the CPU.
+ * We use jiffies here because we want to have a relation
+ * between elapsed time and the blocking of the scheduler.
+ */
+ if (time_is_before_jiffies(start+1))
+ schedule();
}
return -ETIMEDOUT;
}

static inline int
-mmc_spi_wait_unbusy(struct mmc_spi_host *host, ktime_t timeout)
+mmc_spi_wait_unbusy(struct mmc_spi_host *host, unsigned long timeout)
{
return mmc_spi_skip(host, timeout, sizeof(host->data->status), 0);
}

-static int mmc_spi_readtoken(struct mmc_spi_host *host, ktime_t timeout)
+static int mmc_spi_readtoken(struct mmc_spi_host *host, unsigned long timeout)
{
return mmc_spi_skip(host, timeout, 1, 0xff);
}
@@ -607,7 +610,7 @@ mmc_spi_setup_data_message(
*/
static int
mmc_spi_writeblock(struct mmc_spi_host *host, struct spi_transfer *t,
- ktime_t timeout)
+ unsigned long timeout)
{
struct spi_device *spi = host->spi;
int status, i;
@@ -712,7 +715,7 @@ mmc_spi_writeblock(struct mmc_spi_host *
*/
static int
mmc_spi_readblock(struct mmc_spi_host *host, struct spi_transfer *t,
- ktime_t timeout)
+ unsigned long timeout)
{
struct spi_device *spi = host->spi;
int status;
@@ -802,7 +805,7 @@ mmc_spi_data_do(struct mmc_spi_host *hos
unsigned n_sg;
int multiple = (data->blocks > 1);
u32 clock_rate;
- ktime_t timeout;
+ unsigned long timeout;

if (data->flags & MMC_DATA_READ)
direction = DMA_FROM_DEVICE;
@@ -816,8 +819,11 @@ mmc_spi_data_do(struct mmc_spi_host *hos
else
clock_rate = spi->max_speed_hz;

- timeout = ktime_add_ns(ktime_set(0, 0), data->timeout_ns +
- data->timeout_clks * 1000000 / clock_rate);
+ timeout = data->timeout_ns +
+ data->timeout_clks * 1000000 / clock_rate;
+ timeout = usecs_to_jiffies((unsigned int)(timeout / 1000));
+ if (!timeout)
+ timeout = 1;

/* Handle scatterlist segments one at a time, with synch for
* each 512-byte block
---
regards
i. A. Wolfgang Mües
--
Auerswald GmbH & Co. KG
Hardware Development
Telefon: +49 (0)5306 9219 0
Telefax: +49 (0)5306 9219 94
E-Mail: Wolfgang.Mues@Auerswald.de
Web: http://www.auerswald.de
 
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