Re: [PATCH v5 3/5] cdx: add support for bus enable and disable

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Sep 22, 2023 at 03:48:26PM +0530, Abhijit Gangurde wrote:
> CDX bus needs to be disabled before updating/writing devices
> in the FPGA. Once the devices are written, the bus shall be
> rescanned. This change provides sysfs entry to enable/disable the
> CDX bus.
> 
> Co-developed-by: Nipun Gupta <nipun.gupta@amd.com>
> Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
> Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
> Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
> Tested-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
> ---
>  Changes in v5:
>  - Rebased on Linux 6.6
> 
>  Changes in v4:
>  - Add sparse marking for lock around cdx_find_controller() function
> 
>  Changes in v3:
>  - Use platform bus to locate controller
> 
>  Changes in v2:
>  - Improve documentation
>  - Split sysfs entry enable to enable and disable
>  - sysfs entry enable and disable take bus number as an argument
> 
>  Documentation/ABI/testing/sysfs-bus-cdx | 27 +++++++
>  drivers/cdx/cdx.c                       | 97 +++++++++++++++++++++++++
>  drivers/cdx/controller/cdx_controller.c | 50 +++++++++++++
>  drivers/cdx/controller/mc_cdx_pcol.h    | 54 ++++++++++++++
>  drivers/cdx/controller/mcdi_functions.c | 24 ++++++
>  drivers/cdx/controller/mcdi_functions.h | 18 +++++
>  include/linux/cdx/cdx_bus.h             | 12 +++
>  7 files changed, 282 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cdx b/Documentation/ABI/testing/sysfs-bus-cdx
> index 7af477f49998..04c8dfe7e201 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cdx
> +++ b/Documentation/ABI/testing/sysfs-bus-cdx
> @@ -11,6 +11,33 @@ Description:
>  
>  		  # echo 1 > /sys/bus/cdx/rescan
>  
> +What:		/sys/bus/cdx/enable
> +Date:		July 2023
> +Contact:	nipun.gupta@amd.com
> +Description:
> +		Writing bus number in hex to this file will attempt to enable
> +		the CDX bus. The bus number for the cdx devices can be found
> +		at /sys/bus/cdx/devices/cdx-BB:DD, where BB denotes the bus
> +		number for the respective device.
> +
> +		For example ::
> +
> +		  # echo 00 > /sys/bus/cdx/enable
> +
> +What:		/sys/bus/cdx/disable
> +Date:		July 2023
> +Contact:	nipun.gupta@amd.com
> +Description:
> +		Writing bus number in hex to this file will attempt to disable
> +		the CDX bus. CDX bus should be disabled before updating the
> +		devices in FPGA. The bus number for the cdx devices can be
> +		found at /sys/bus/cdx/devices/cdx-BB:DD, where BB denotes the
> +		bus number for the respective device.
> +
> +		For example ::
> +
> +		  # echo 00 > /sys/bus/cdx/disable
> +

I can't remember, but why aren't these just attributes on the bus
controller for that specific bus, and not a bus-wide attribute?
Wouldn't that make more sense and remove the need for parsing values of
a bus number and make it more obvious what bus was and was not enabled
at any point in time (i.e. you can't read to see what bus is
enabled/disabled right now with this change.)

thanks,

greg k-h