From: Miod Vallat <miod@online.fr>
Subject: Re: uhidev fix for set report output command
To: Marcus Glocker <marcus@nazgul.ch>
Cc: tech@openbsd.org
Date: Tue, 7 Jan 2025 11:01:31 +0000

> Feedback, OKs?

It is probably worth moving lines 434-448, which setup cmd[2], into the
if, since setting dataoff to zero in the else part makes that assignment
pointless.

> Index: sys/dev/i2c/ihidev.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/i2c/ihidev.c,v
> diff -u -p -u -p -r1.35 ihidev.c
> --- sys/dev/i2c/ihidev.c	6 Jan 2025 02:13:55 -0000	1.35
> +++ sys/dev/i2c/ihidev.c	6 Jan 2025 20:40:39 -0000
> @@ -453,6 +453,22 @@ ihidev_hid_command(struct ihidev_softc *
>  			cmd[dataoff++] = htole16(sc->hid_desc.wDataRegister)
>  			    >> 8;
>  		} else {
> +			/*
> +			 * When using the wOutputRegister for a set report
> +			 * output command, the wCommandRegister command needs
> +			 * to be omitted, and we write the report data straight
> +			 * in to the wOutputRegister:
> +			 *
> +			 * cmd[0] = wOutputRegister (LSB)
> +			 * cmd[1] = wOutputRegister (MSB)
> +			 * cmd[2] = Length Field (LSB)
> +			 * cmd[3] = Length Field (MSB)
> +			 * cmd[4] = Report ID
> +			 * cmd[5] = DATA
> +			 * ...
> +			 */
> +			cmdlen = 5;
> +			dataoff = 0;
>  			cmd[dataoff++] = htole16(sc->hid_desc.wOutputRegister)
>  			    & 0xff;
>  			cmd[dataoff++] = htole16(sc->hid_desc.wOutputRegister)
>