linux-kernel - Re: [PATCH v2 03/11] mux: core: Add usb.h header with MUX_USB_* and and MUX_TYPEC

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Date:   Fri, 8 Sep 2017 17:47:12 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Hans de Goede <hdegoede@...hat.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Mathias Nyman <mathias.nyman@...el.com>
Cc:     linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy Natarajan <sathyaosid@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 03/11] mux: core: Add usb.h header with MUX_USB_* and
 and MUX_TYPEC_* state constants

On 2017-09-05 18:42, Hans de Goede wrote:
> Add MUX_USB_* and MUX_TYPEC_* state constant defines, which can be used by
> USB device/host, resp. Type-C polarity/role/altmode mux drivers and
> consumers to ensure that they agree on the meaning of the
> mux_control_select() state argument.
> 
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
> Changes in v2:
> -Start numbering of defines at 0 not 1
> -Use a new usb.h header, rather then adding these to consumer.h
> -Add separate MUX_USB_* and MUX_TYPEC_* defines
> ---
>  include/linux/mux/usb.h | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>  create mode 100644 include/linux/mux/usb.h
> 
> diff --git a/include/linux/mux/usb.h b/include/linux/mux/usb.h
> new file mode 100644
> index 000000000000..44df5eca5256
> --- /dev/null
> +++ b/include/linux/mux/usb.h
> @@ -0,0 +1,32 @@
> +/*
> + * mux/usb.h - definitions for USB multiplexers
> + *
> + * Copyright (C) 2017 Hans de Goede <hdegoede@...hat.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#ifndef _LINUX_MUX_USB_H
> +#define _LINUX_MUX_USB_H
> +
> +/* Mux state values for USB device/host role muxes */
> +#define MUX_USB_DEVICE		(0) /* USB device mode */
> +#define MUX_USB_HOST		(1) /* USB host mode */
> +#define MUX_USB_STATES		(2)
> +
> +/*
> + * Mux state values for Type-C polarity/role/altmode muxes.
> + *
> + * MUX_TYPEC_POLARITY_INV may be or-ed together with any other mux-state as
> + * inverted-polarity (Type-C plugged in upside down) can happen with any
> + * other mux-state.
> + */
> +#define MUX_TYPEC_POLARITY_INV		BIT(0)   /* Polarity inverted bit */
> +#define MUX_TYPEC_DEVICE		(0 << 1) /* USB device mode */
> +#define MUX_TYPEC_HOST			(1 << 1) /* USB host mode */
> +#define MUX_TYPEC_HOST_AND_DP_SRC	(2 << 1) /* USB host + 2 lanes DP src */
> +#define MUX_TYPEC_DP_SRC		(3 << 1) /* 4 lanes Display Port src */
> +#define MUX_TYPEC_STATES		(4 << 1)

But USB Type-C muxes need not support just these states If I read it right?
USB Type-C seems to be usable for a variety of protocols and the above list
seems pretty much like a special case for this mux (and perhaps a set of
other similar muxes). But when someone with a USB Type-C mux for different
protocols shows up, that person will probably be frustrated by these
defines, no? Or is there something I don't see that limits USB-C to DP?

Cheers,
Peter

> +
> +#endif /* _LINUX_MUX_TYPEC_H */
>