linux-kernel - Re: [PATCH 2/2] soundwire: bus: Add internal slave ID and use for IRQs

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Message-ID: <aAeHgqcQCtuFKW/A@opensource.cirrus.com>
Date: Tue, 22 Apr 2025 13:11:46 +0100
From: Charles Keepax <ckeepax@...nsource.cirrus.com>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>
Cc: vkoul@...nel.org, yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com,
        linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com
Subject: Re: [PATCH 2/2] soundwire: bus: Add internal slave ID and use for
 IRQs

On Tue, Apr 22, 2025 at 01:50:13PM +0200, Pierre-Louis Bossart wrote:
> On 4/22/25 12:42, Charles Keepax wrote:
> I see the patch add a limit during probe, so now that
> means the number of ACPI devices MUST be lower than 11. That
> doesn't sound right to me and could cause some configurations
> to fail. It's perfectly ok to have ghost devices and no limits
> on how many our BIOS colleagues decide to list.

Yeah it will limit the ACPI to 11 devices. I can't say I am a
huge fan of the "ghost" devices, like its ACPI it is for
describing the hardware, so it should describe the hardware.

That said my thinking on this was I have not seen a system with
more than 4 real devices on a single bus, and not more than a
couple ghosts in the ACPI. So this didn't look like a big issue.

> Using a dedicated IDA for IRQ mapping looks like a good
> idea to me, but I don't think you can really use the same IDA
> for dev_num

If you are really concerned about the ghost devices I could back
out the part that reuses the ID for the dev_num. However I do
need to know the maximum number of devices when the IRQ domain is
allocated. So I can't really see a way to avoid picking a maximum
number of devices for the bus. What number of real + ghosts would
you be comfortable with? Although I guess if not using it for the
dev_num it is then fairly easy to expand if needed so perhaps I
just back out the dev_num bit, but stick with 11 for now and we
can expand if necessary?

Thanks,
Charles