There have been few discussions in the past about how to handle SPI controller
limitations like max message length. However they don't seem to have resulted
in accepted patches yet.
I also stumbled across this topic because I own a device using Freescale's
ESPI which has a 64K message size limitation.
At least one agreed fact is that silently assembling chunks in protocol
drivers is not the preferred approach.
Maybe a better approach would be to introduce a new member of spi_master
dealing with controller limitations.
My issue is just the message size limitation but most likely there are more
and different limitations in other controllers.
I'd introduce a struct spi_controller_restrictions and add a member to
spi_master
pointing to such a struct. Then a controller driver could do something like
this:
static const struct spi_controller_restrictions fsl_espi_restrictions = {
.max_msg_size = 0xffff,
};
master->restrictions = &fsl_espi_restrictions;
I also add an example how a protocol driver could use this extension.
Appreciate any comment.
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 269e8af..8a27c66 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -276,6 +276,17 @@ static inline void spi_unregister_driver(struct spi_driver
*sdrv)
spi_unregister_driver)
/**
+ * struct spi_controller_restrictions - restrictions of the controller
+ * @max_msg_size: maximum length of a SPI message
+ * SPI controllers can have different restrictions like a maximum
+ * supported message size.
+ * This struct most likely is going to be extended over time.
+ */
+struct spi_controller_restrictions {
+ size_t max_msg_size;
+};
+
+/**
* struct spi_master - interface to SPI master controller
* @dev: device interface to this driver
* @list: link with the global spi_master list
@@ -295,6 +306,7 @@ static inline void spi_unregister_driver(struct spi_driver
*sdrv)
* @min_speed_hz: Lowest supported transfer speed
* @max_speed_hz: Highest supported transfer speed
* @flags: other constraints relevant to this driver
+ * @restrictions: controller restrictions like max supported message size
* @bus_lock_spinlock: spinlock for SPI bus locking
* @bus_lock_mutex: mutex for SPI bus locking
* @bus_lock_flag: indicates that the SPI bus is locked for exclusive use
@@ -417,6 +429,9 @@ struct spi_master {
#define SPI_MASTER_MUST_RX BIT(3) /* requires rx */
#define SPI_MASTER_MUST_TX BIT(4) /* requires tx */
+ /* collection of restrictions like max supported message size */
+ struct spi_controller_restrictions *restrictions;
+
/* lock and mutex for SPI bus locking */
spinlock_t bus_lock_spinlock;
struct mutex bus_lock_mutex;
--
2.6.2
---
drivers/mtd/devices/m25p80.c | 41 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 36 insertions(+), 5 deletions(-)
diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
index f10daa8..0e46fb1f 100644
--- a/drivers/mtd/devices/m25p80.c
+++ b/drivers/mtd/devices/m25p80.c
@@ -115,11 +115,7 @@ static inline unsigned int m25p80_rx_nbits(struct spi_nor
*nor)
}
}
-/*
- * Read an address range from the nor chip. The address range
- * may be any size provided it is within the physical boundaries.
- */
-static int m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
+static int _m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
size_t *retlen, u_char *buf)
{
struct m25p *flash = nor->priv;
@@ -160,6 +156,41 @@ static int m25p80_read(struct spi_nor *nor, loff_t from,
size_t len,
return ret;
}
+/*
+ * Read an address range from the nor chip. The address range
+ * may be any size provided it is within the physical boundaries.
+ */
+static int m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
+ size_t *retlen, u_char *buf)
+{
+ struct m25p *flash = nor->priv;
+ struct spi_controller_restrictions *restrictions =
+ flash->spi->master->restrictions;
+ size_t cmd_len, xfer_len, max_len;
+ int ret = 0;
+
+ /* convert the dummy cycles to the number of bytes */
+ cmd_len = m25p_cmdsz(nor) + nor->read_dummy / 8;
+
+ max_len = (restrictions && restrictions->max_msg_size) ?
+ restrictions->max_msg_size : SIZE_MAX;
+
+ if (unlikely(max_len < cmd_len))
+ return -EINVAL;
+
+ max_len -= cmd_len;
+
+ while (len) {
+ xfer_len = min(len, max_len);
+ ret = _m25p80_read(nor, from, xfer_len, retlen, buf);
+ if (ret < 0)
+ break;
+ from += xfer_len;
+ len -= xfer_len;
+ }
+
+ return ret;
+}
+
static int m25p80_erase(struct spi_nor *nor, loff_t offset)
{
struct m25p *flash = nor->priv;
--
2.6.2
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