Re: [PATCH 09/15] ASoC: SDCA: Add UMP buffer helper functions

[Charles Keepax <ckeepax@opensource.cirrus.com>]

On Mon, Sep 08, 2025 at 02:02:09PM +0200, Pierre-Louis Bossart wrote:
> On 9/5/25 16:31, Charles Keepax wrote:
> > Add helper functions for handling Universal Message Passing (UMP)
> > buffers on SDCA devices. These are generic mechanisms to pass blocks of
> > binary data between the host and the device, in both directions. They
> > are used for things like passing HID descriptors and the File Download
> > process.
> 
> Humm, these helpers are very host-centric and don't seem to cover the basic
> UMP message passing, e.g. for host to device:
> 
> 1. host puts information in a buffer.

by calling sdca_ump_write_message

> 2. host sets ownership to device and waits for ownership to be returned.

by calling sdca_ump_set_owner_device

> 3. device does a bunch of things and returns the ownership to the host.
> 4. host detects ownership change or times out with a failed transfer error message.

by receiving an IRQ on the owner control.

> What am I missing?

You might need to elaborate a little more on what you think is
missing. The four functions implement the four operations that
power a UMP buffer, checking you have ownership, passing
ownership back to the device, reading data, and writing data.

One could combine more of the functionality into a single helper,
but then you start to hit problems where you need to do extra
bits.

For example HID, very simple just: check you own the buffer,
read the message, and pass the buffer back.

FDL, has extra steps: check you own the buffer, check the FDL
status, then write the buffer, then write the FDL response,
and only then pass the buffer back.

Thanks,
Charles