linux-kernel - Re: [PATCH v5 02/16] phy: Distinguish between Rx and Tx for MIPI D-PHY with submodes

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Message-ID: <YK5aAL6ciI92ruHs@aptenodytes>
Date:   Wed, 26 May 2021 16:24:00 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-sunxi@...glegroups.com
Cc:     Yong Deng <yong.deng@...ewell.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonathan Corbet <corbet@....net>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Helen Koike <helen.koike@...labora.com>,
        Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        kevin.lhopital@...mail.com,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v5 02/16] phy: Distinguish between Rx and Tx for MIPI
 D-PHY with submodes

Hi everyone,

On Fri 15 Jan 21, 21:01, Paul Kocialkowski wrote:
> As some D-PHY controllers support both Rx and Tx mode, we need a way for
> users to explicitly request one or the other. For instance, Rx mode can
> be used along with MIPI CSI-2 while Tx mode can be used with MIPI DSI.
> 
> Introduce new MIPI D-PHY PHY submodes to use with PHY_MODE_MIPI_DPHY.
> The default (zero value) is kept to Tx so only the rkisp1 driver, which
> uses D-PHY in Rx mode, needs to be adapted.

I think it was Laurent who brought up on IRC that using a submode is probably
not a correct way to distinguish between Rx and Tx modes.

Thinking about it again, it feels like selecting the direction at run-time
would only be relevant if there's D-PHY hardware than can do both Tx and Rx
*and* that can be muxed to either a MIPI DSI and a CSI-2 controller at
run-time.

For the Allwinner case, the D-PHY is the same hardware for both but there will
be one instance attached to each controller, not a single shared instance.
It feels rather unlikely that a device with both MIPI DSI and CSI-2 would only
have one PHY for the two as this wouldn't allow concurrent use of the two
controllers. Even in a case where there'd be n controllers and m < n
bi-directional PHYs, it feels safe to assume that a static attribution would
be sufficient.
 
As a result it feels more relevant to have this distinction in device-tree
rather than via the PHY API.

What do you think?
Any suggestion on how this should be represented in device-tree?

Cheers,

Paul

> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> Acked-by: Helen Koike <helen.koike@...labora.com>
> ---
>  drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c |  3 ++-
>  include/linux/phy/phy-mipi-dphy.h                   | 13 +++++++++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c b/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c
> index 2e5b57e3aedc..cab261644102 100644
> --- a/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c
> +++ b/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c
> @@ -948,7 +948,8 @@ static int rkisp1_mipi_csi2_start(struct rkisp1_isp *isp,
>  
>  	phy_mipi_dphy_get_default_config(pixel_clock, isp->sink_fmt->bus_width,
>  					 sensor->lanes, cfg);
> -	phy_set_mode(sensor->dphy, PHY_MODE_MIPI_DPHY);
> +	phy_set_mode_ext(cdev->dphy, PHY_MODE_MIPI_DPHY,
> +			 PHY_MIPI_DPHY_SUBMODE_RX);
>  	phy_configure(sensor->dphy, &opts);
>  	phy_power_on(sensor->dphy);
>  
> diff --git a/include/linux/phy/phy-mipi-dphy.h b/include/linux/phy/phy-mipi-dphy.h
> index a877ffee845d..0f57ef46a8b5 100644
> --- a/include/linux/phy/phy-mipi-dphy.h
> +++ b/include/linux/phy/phy-mipi-dphy.h
> @@ -6,6 +6,19 @@
>  #ifndef __PHY_MIPI_DPHY_H_
>  #define __PHY_MIPI_DPHY_H_
>  
> +/**
> + * enum phy_mipi_dphy_submode - MIPI D-PHY sub-mode
> + *
> + * A MIPI D-PHY can be used to transmit or receive data.
> + * Since some controllers can support both, the direction to enable is specified
> + * with the PHY sub-mode. Transmit is assumed by default with phy_set_mode.
> + */
> +
> +enum phy_mipi_dphy_submode {
> +	PHY_MIPI_DPHY_SUBMODE_TX = 0,
> +	PHY_MIPI_DPHY_SUBMODE_RX,
> +};
> +
>  /**
>   * struct phy_configure_opts_mipi_dphy - MIPI D-PHY configuration set
>   *
> -- 
> 2.30.0
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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