Re: [PATCH 0/6] mailbox: arm_mhu: add support for subchannels

From: Jassi Brar
Date: Tue May 02 2017 - 23:19:02 EST

Hi Sudeep,

On Tue, May 2, 2017 at 7:25 PM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> Hi Jassi,
> This series adds subchannel support to ARM MHU mailbox controller
> driver. Since SCPI never used second slot, we were able to use the
> existing driver as is. However, that's changing soon and the new
> SCMI protocol under development needs subchannel support. If you
> recall when you initially added this driver, I was pushing for some
> of these changes like threaded irq. This patch series adds support
> for the subchannels on ARM MHU controllers.
There are really no "sub-channels" in the ARM MHU controller. There
are exactly three channels that work on 32bit registers. The SET/CLEAR
registers are there to prevent races between local and remote
firmware, and not to emulate virtual channels operating on single
bits. Please remember all 32-bits work together to generate one

You arrived at the "sub-channel" idea only because your protocol uses
1-bit messages. This patchset seems rather regressive - reduce from
2^32 possible signals to mere 32, by bloating the MHU driver.

If it's difficult to see how your protocol can be implemented over
existing controller driver, please let me know.