From: Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: fix dwhdmi builtin i2c adapter
To: Jonathan Matthew <jonathan@d14n.org>
Cc: tech@openbsd.org, kettenis@openbsd.org
Date: Sun, 23 Mar 2025 15:54:36 +0100

> Date: Sun, 23 Mar 2025 23:07:45 +1000
> From: Jonathan Matthew <jonathan@d14n.org>
> 
> Looking into rkdwhdmi(4) a bit, I found that the builtin i2c adapter in the
> dwhdmi code is lacking ic_acquire_bus and ic_release_bus functions, which
> are called unconditionally by the drm edid code (see i2c_master_xfer() in
> drm_linux.c), so if you have an rkdwhdmi device with no ddc-i2c-bus property,
> like most RK356x devices, it crashes during drm mode probing.
> 
> Can we assume that if the HDMI DDC bus is connected to the builtin i2c
> in the HDMI TX device, we don't need to do anything to acquire or release
> the bus?

Probably.  I think the DRM code has some other mechanisms to prevent
multiple DDC reads from happening at the same time.

> ok?

ok kettenis@

> Index: dwhdmi.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/ic/dwhdmi.c,v
> diff -u -p -r1.5 dwhdmi.c
> --- dwhdmi.c	16 Jan 2024 23:37:50 -0000	1.5
> +++ dwhdmi.c	23 Mar 2025 12:01:21 -0000
> @@ -251,6 +251,17 @@ enum dwhdmi_dai_mixer_ctrl {
>  };
>  
>  int
> +dwhdmi_ddc_acquire_bus(void *priv, int flags)
> +{
> +	return 0;
> +}
> +
> +void
> +dwhdmi_ddc_release_bus(void *priv, int flags)
> +{
> +}
> +
> +int
>  dwhdmi_ddc_exec(void *priv, i2c_op_t op, i2c_addr_t addr,
>      const void *cmdbuf, size_t cmdlen, void *buf, size_t len, int flags)
>  {
> @@ -871,6 +882,8 @@ dwhdmi_attach(struct dwhdmi_softc *sc)
>  
>  		memset(ic, 0, sizeof(*ic));
>  		ic->ic_cookie = sc;
> +		ic->ic_acquire_bus = dwhdmi_ddc_acquire_bus;
> +		ic->ic_release_bus = dwhdmi_ddc_release_bus;
>  		ic->ic_exec = dwhdmi_ddc_exec;
>  		sc->sc_ic = ic;
>  	}
> 
>