In addition to providing direct access to SPI bus, some spi controller
hardwares (like ti-qspi) provide special memory mapped port
to accesses SPI flash devices in order to increase read performance.
This means the controller can automatically send the SPI signals
required to read data from the SPI flash device.
For this, spi controller needs to know flash specific information like
read command to use, dummy bytes and address width. Once these settings
are populated in hardware registers, any read accesses to flash's memory
map region(SoC specific) through memcpy (or mem-to mem DMA copy) will be
handled by controller hardware. The hardware will automatically generate
SPI signals required to read data from flash and present it to CPU/DMA.

Introduce spi_mtd_mmap_read() interface to support memory mapped read
over SPI flash devices. SPI master drivers can implement this callback to
support memory mapped read interfaces. m25p80 flash driver and other
flash drivers can call this to request memory mapped read. The interface
should only be used MTD flashes and cannot be used with other SPI devices.

Signed-off-by: Vignesh R <vigneshr@ti.com>
---
 drivers/spi/spi.c       | 35 +++++++++++++++++++++++++++++++++++
 include/linux/spi/spi.h | 23 +++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index a5f53de813d3..5a5c7a7d47f2 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c

@@ -1059,6 +1059,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
                }
        }

+       mutex_lock(&master->mmap_lock_mutex);
        trace_spi_message_start(master->cur_msg);

        if (master->prepare_message) {

@@ -1068,6 +1069,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
                                "failed to prepare message: %d\n", ret);
                        master->cur_msg->status = ret;
                        spi_finalize_current_message(master);
+                       mutex_unlock(&master->mmap_lock_mutex);
                        return;
                }
                master->cur_msg_prepared = true;

@@ -1077,6 +1079,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
        if (ret) {
                master->cur_msg->status = ret;
                spi_finalize_current_message(master);
+               mutex_unlock(&master->mmap_lock_mutex);
                return;
        }

@@ -1084,8 +1087,10 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
        if (ret) {
                dev_err(&master->dev,
                        "failed to transfer one message from queue\n");
+               mutex_unlock(&master->mmap_lock_mutex);
                return;
        }
+       mutex_unlock(&master->mmap_lock_mutex);
 }

 /**

@@ -1732,6 +1737,7 @@ int spi_register_master(struct spi_master *master)
        spin_lock_init(&master->queue_lock);
        spin_lock_init(&master->bus_lock_spinlock);
        mutex_init(&master->bus_lock_mutex);
+       mutex_init(&master->mmap_lock_mutex);
        master->bus_lock_flag = 0;
        init_completion(&master->xfer_completion);
        if (!master->max_dma_len)

@@ -2237,6 +2243,35 @@ int spi_async_locked(struct spi_device *spi, struct spi_message *message)
 EXPORT_SYMBOL_GPL(spi_async_locked);


+int spi_mtd_mmap_read(struct spi_device *spi, loff_t from, size_t len,
+                     size_t *retlen, u_char *buf, u8 read_opcode,
+                     u8 addr_width, u8 dummy_bytes)
+
+{
+       struct spi_master *master = spi->master;
+       int ret;
+
+       if (master->auto_runtime_pm) {
+               ret = pm_runtime_get_sync(master->dev.parent);
+               if (ret < 0) {
+                       dev_err(&master->dev, "Failed to power device: %d\n",
+                               ret);
+                       goto err;
+               }
+       }
+       mutex_lock(&master->mmap_lock_mutex);
+       ret = master->spi_mtd_mmap_read(spi, from, len, retlen, buf,
+                                       read_opcode, addr_width,
+                                       dummy_bytes);
+       mutex_unlock(&master->mmap_lock_mutex);
+       if (master->auto_runtime_pm)
+               pm_runtime_put(master->dev.parent);
+
+err:
+       return ret;
+}
+EXPORT_SYMBOL_GPL(spi_mtd_mmap_read);
+
 /*-------------------------------------------------------------------------*/

 /* Utility methods for SPI master protocol drivers, layered on

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 6b00f18f5e6b..0a6d8ad57357 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h

@@ -297,6 +297,7 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  * @flags: other constraints relevant to this driver
  * @bus_lock_spinlock: spinlock for SPI bus locking
  * @bus_lock_mutex: mutex for SPI bus locking
+ * @mmap_lock_mutex: mutex for locking SPI bus when mmap transfer is on.