| Message ID | 1502538843-3283-1-git-send-email-vicky773@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Aug 12, 2017 at 05:24:03PM +0530, Vikram N wrote: > else > - status = spi_sync(spi, message); > + status = spidev->bus_locked ? spi_sync_locked(spi, message) : > + spi_sync(spi, message); Please don't abuse the ternery operator, people need to be able to read the code. > + case SPI_IOC_BUS_LOCK: > + spi_bus_lock(spi->master); > + spidev->bus_locked = true; > + break; > + > + case SPI_IOC_BUS_UNLOCK: > + spi_bus_unlock(spi->master); > + spidev->bus_locked = false; > + break; I'm not super convinced that this API is a good idea in general - it seems extremely niche to be using multiple userspace programs that don't need to coordinate at all except for a single lock (which they will all need to use to avoid just bouncing off with errors). That all seems very narrow. I'm also worried that even if there is such a use case this code is very fragile as it stands. If an application crashes then nothing will free a lock it holds and any application can through simple error drop locks that are supposed to be held by other applications. This isn't going to be terribly robust.
diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c index cda1071..d14a8c1 100644 --- a/drivers/spi/spidev.c +++ b/drivers/spi/spidev.c @@ -85,6 +85,7 @@ struct spidev_data { u8 *tx_buffer; u8 *rx_buffer; u32 speed_hz; + bool bus_locked; }; static LIST_HEAD(device_list); @@ -109,7 +110,8 @@ struct spidev_data { if (spi == NULL) status = -ESHUTDOWN; else - status = spi_sync(spi, message); + status = spidev->bus_locked ? spi_sync_locked(spi, message) : + spi_sync(spi, message); if (status == 0) status = message->actual_length; @@ -462,6 +464,16 @@ static int spidev_message(struct spidev_data *spidev, } break; + case SPI_IOC_BUS_LOCK: + spi_bus_lock(spi->master); + spidev->bus_locked = true; + break; + + case SPI_IOC_BUS_UNLOCK: + spi_bus_unlock(spi->master); + spidev->bus_locked = false; + break; + default: /* segmented and/or full-duplex I/O request */ /* Check message and copy into scratch area */ diff --git a/include/uapi/linux/spi/spidev.h b/include/uapi/linux/spi/spidev.h index dd5f21e..1f776fe 100644 --- a/include/uapi/linux/spi/spidev.h +++ b/include/uapi/linux/spi/spidev.h @@ -136,6 +136,8 @@ struct spi_ioc_transfer { #define SPI_IOC_RD_MODE32 _IOR(SPI_IOC_MAGIC, 5, __u32) #define SPI_IOC_WR_MODE32 _IOW(SPI_IOC_MAGIC, 5, __u32) - +/* Exclusive bus access lock */ +#define SPI_IOC_BUS_LOCK _IO(SPI_IOC_MAGIC, 6) +#define SPI_IOC_BUS_UNLOCK _IO(SPI_IOC_MAGIC, 7) #endif /* SPIDEV_H */
There are use-cases wherein one or more applications wants to communicate with the same spi slave chip and they wish to have exclusive bus access. May to serialize their command,response patterns. This can be realized in two ways, - Identify different applications using same spi channel and implement synchronization mechanisms to get exclusive bus access - Provide some mechanism through spidev driver to get exclusive spi bus access like via ioctls This patch implements the second approach which eliminates the need for implementing complex IPC mechanisms in the applications which shares the spi bus. This becomes even harder if we don't have access to the source code of the application which is using the spi channel. Signed-off-by: Vikram N <vicky773@gmail.com> --- drivers/spi/spidev.c | 14 +++++++++++++- include/uapi/linux/spi/spidev.h | 4 +++- 2 files changed, 16 insertions(+), 2 deletions(-)