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From:   Pin-yen Lin <treapking@chromium.org>
Date:   Thu, 12 Jan 2023 13:48:09 +0800
Message-ID: <CAEXTbpfrZCD-53wx2RaboH4rYPF7qm7TrhxyN80k++CZ2UqTKA@mail.gmail.com>
Subject: Re: [PATCH v10 3/9] drm/display: Add Type-C switch helpers
To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc:     Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Robert Foss <robert.foss@linaro.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Daniel Scally <djrscally@gmail.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Prashant Malani <pmalani@chromium.org>,
        Benson Leung <bleung@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>,
        =?UTF-8?B?TsOtY29sYXMgRiAuIFIgLiBBIC4gUHJhZG8=?= 
        <nfraprado@collabora.com>, Marek Vasut <marex@denx.de>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Javier Martinez Canillas <javierm@redhat.com>,
        Lyude Paul <lyude@redhat.com>, chrome-platform@lists.linux.dev,
        Xin Ji <xji@analogixsemi.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        linux-kernel@vger.kernel.org, Allen Chen <allen.chen@ite.com.tw>,
        linux-acpi@vger.kernel.org, Hsin-Yi Wang <hsinyi@chromium.org>,
        Chen-Yu Tsai <wenst@chromium.org>,
        Douglas Anderson <dianders@chromium.org>,
        Imre Deak <imre.deak@intel.com>,
        Jani Nikula <jani.nikula@intel.com>,
        Kees Cook <keescook@chromium.org>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        shaomin Deng <dengshaomin@cdjrlc.com>
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On Thu, Jan 12, 2023 at 1:24 PM Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On 12/01/2023 07:19, Pin-yen Lin wrote:
> > Hi Dmitry,
> >
> > Thanks for the review.
> >
> > On Thu, Jan 12, 2023 at 12:40 PM Dmitry Baryshkov
> > <dmitry.baryshkov@linaro.org> wrote:
> >>
> >> On 12/01/2023 06:20, Pin-yen Lin wrote:
> >>> Add helpers to register and unregister Type-C "switches" for bridges
> >>> capable of switching their output between two downstream devices.
> >>>
> >>> The helper registers USB Type-C mode switches when the "mode-switch"
> >>> and the "data-lanes" properties are available in Device Tree.
> >>>
> >>> Signed-off-by: Pin-yen Lin <treapking@chromium.org>
> >>> Tested-by: Chen-Yu Tsai <wenst@chromium.org>
> >>> Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
> >>> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> >>>
> >>> ---
> >>>
> >>> Changes in v10:
> >>> - Collected Reviewed-by and Tested-by tags
> >>> - Replaced "void *" with "typec_mux_set_fn_t" for mux_set callbacks
> >>> - Print out the node name when errors on parsing DT
> >>> - Use dev_dbg instead of dev_warn when no Type-C switch nodes available
> >>> - Made the return path of drm_dp_register_mode_switch clearer
> >>>
> >>> Changes in v8:
> >>> - Fixed the build issue when CONFIG_TYPEC=m
> >>> - Fixed some style issues
> >>>
> >>> Changes in v7:
> >>> - Extracted the common codes to a helper function
> >>> - New in v7
> >>>
> >>>    drivers/gpu/drm/display/drm_dp_helper.c | 134 ++++++++++++++++++++++++
> >>>    include/drm/display/drm_dp_helper.h     |  17 +++
> >>>    2 files changed, 151 insertions(+)
> >>>
> >>> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> >>> index 16565a0a5da6..a2ec40a621cb 100644
> >>> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> >>> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> >>> @@ -30,11 +30,13 @@
> >>>    #include <linux/sched.h>
> >>>    #include <linux/seq_file.h>
> >>>    #include <linux/string_helpers.h>
> >>> +#include <linux/usb/typec_mux.h>
> >>>    #include <linux/dynamic_debug.h>
> >>>
> >>>    #include <drm/display/drm_dp_helper.h>
> >>>    #include <drm/display/drm_dp_mst_helper.h>
> >>>    #include <drm/drm_edid.h>
> >>> +#include <drm/drm_of.h>
> >>>    #include <drm/drm_print.h>
> >>>    #include <drm/drm_vblank.h>
> >>>    #include <drm/drm_panel.h>
> >>> @@ -3891,3 +3893,135 @@ int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux)
> >>>    EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
> >>>
> >>>    #endif
> >>> +
> >>> +#if IS_REACHABLE(CONFIG_TYPEC)
> >>> +static int drm_dp_register_mode_switch(struct device *dev, struct device_node *node,
> >>> +                                    struct drm_dp_typec_switch_desc *switch_desc,
> >>> +                                    void *data, typec_mux_set_fn_t mux_set)
> >>> +{
> >>> +     struct drm_dp_typec_port_data *port_data;
> >>> +     struct typec_mux_desc mux_desc = {};
> >>> +     char name[32];
> >>> +     u32 dp_lanes[2];
> >>> +     int ret, num_lanes, port_num = -1;
> >>> +
> >>> +     num_lanes = drm_of_get_data_lanes_count(node, 0, 2);
> >>
> >> 2 looks incorrect. IIRC DP altmode can support up to 4 lanes.
> >
> > This function is implemented for 4-lane DP bridges to switch its
> > outputs between 2 downstreams. So, I assume that there will only be at
> > most 2 lanes for each downstream. I don't think a 4-lane downstream
> > makes sense for mode switches unless we want to support bridges with
> > more than 4 lanes.
>
> Yes. However by using 4 here you'd make the helper generic and cover
> both your case and the generic case. We don't need this for the msm case
> (since the mux is handled by the PHY). But if not for the PHY, I'd have
> used such helper (with max_lanes = 4).
>
I wonder if simply using 4 here really makes it more generic here.
This function assumes the mapping between "data-lanes" and the port
number (e.g., 0/1 --> port 0) and hard-coded the way to parse the
property.

Is it better to use "reg" instead of "data-lanes" to determine the
port number? The drivers can still read the DT node to get the
"data-lanes" property if they want to do some fancy stuffs around
that.
> >>
> >>> +     if (num_lanes <= 0) {
> >>> +             dev_err(dev, "Error on getting data lanes count from %s: %d\n",
> >>> +                     node->name, num_lanes);
> >>> +             return num_lanes;
> >>> +     }
> >>> +
> >>> +     ret = of_property_read_u32_array(node, "data-lanes", dp_lanes, num_lanes);
> >>> +     if (ret) {
> >>> +             dev_err(dev, "Failed to read the data-lanes variable from %s: %d\n",
> >>> +                     node->name, ret);
> >>> +             return ret;
> >>> +     }
> >>> +
> >>> +     port_num = dp_lanes[0] / 2;
> >>> +
> >>> +     port_data = &switch_desc->typec_ports[port_num];
> >>> +     port_data->data = data;
> >>> +     mux_desc.fwnode = &node->fwnode;
> >>> +     mux_desc.drvdata = port_data;
> >>> +     snprintf(name, sizeof(name), "%s-%u", node->name, port_num);
> >>> +     mux_desc.name = name;
> >>> +     mux_desc.set = mux_set;
> >>> +
> >>> +     port_data->typec_mux = typec_mux_register(dev, &mux_desc);
> >>> +     if (IS_ERR(port_data->typec_mux)) {
> >>> +             ret = PTR_ERR(port_data->typec_mux);
> >>> +             dev_err(dev, "Mode switch register for port %d failed: %d\n",
> >>> +                     port_num, ret);
> >>> +
> >>> +             return ret;
> >>> +     }
> >>> +
> >>> +     return 0;
> >>> +}
> >>> +
> >>> +/**
> >>> + * drm_dp_register_typec_switches() - register Type-C switches
> >>> + * @dev: Device that registers Type-C switches
> >>> + * @port: Device node for the switch
> >>> + * @switch_desc: A Type-C switch descriptor
> >>> + * @data: Private data for the switches
> >>> + * @mux_set: Callback function for typec_mux_set
> >>> + *
> >>> + * This function registers USB Type-C switches for DP bridges that can switch
> >>> + * the output signal between their output pins.
> >>> + *
> >>> + * Currently only mode switches are implemented, and the function assumes the
> >>> + * given @port device node has endpoints with "mode-switch" property.
> >>> + * Register the endpoint as port 0 if the "data-lanes" property falls in 0/1,
> >>> + * and register it as port 1 if "data-lanes" falls in 2/3.
> >>> + */
> >>> +int drm_dp_register_typec_switches(struct device *dev, struct device_node *port,
> >>> +                                struct drm_dp_typec_switch_desc *switch_desc,
> >>> +                                void *data, typec_mux_set_fn_t mux_set)
> >>> +{
> >>> +     struct device_node *sw;
> >>> +     int ret;
> >>> +
> >>> +     for_each_child_of_node(port, sw) {
> >>> +             if (of_property_read_bool(sw, "mode-switch"))
> >>> +                     switch_desc->num_typec_switches++;
> >>> +     }
> >>> +
> >>> +     if (!switch_desc->num_typec_switches) {
> >>> +             dev_dbg(dev, "No Type-C switches node found\n");
> >>> +             return 0;
> >>> +     }
> >>> +
> >>> +     switch_desc->typec_ports = devm_kcalloc(
> >>> +             dev, switch_desc->num_typec_switches,
> >>> +             sizeof(struct drm_dp_typec_port_data), GFP_KERNEL);
> >>> +
> >>> +     if (!switch_desc->typec_ports)
> >>> +             return -ENOMEM;
> >>> +
> >>> +     /* Register switches for each connector. */
> >>> +     for_each_child_of_node(port, sw) {
> >>> +             if (!of_property_read_bool(sw, "mode-switch"))
> >>> +                     continue;
> >>> +             ret = drm_dp_register_mode_switch(dev, sw, switch_desc, data, mux_set);
> >>> +             if (ret)
> >>> +                     goto err_unregister_typec_switches;
> >>> +     }
> >>> +
> >>> +     return 0;
> >>> +
> >>> +err_unregister_typec_switches:
> >>> +     of_node_put(sw);
> >>> +     drm_dp_unregister_typec_switches(switch_desc);
> >>> +     dev_err(dev, "Failed to register mode switch: %d\n", ret);
> >>> +     return ret;
> >>> +}
> >>> +EXPORT_SYMBOL(drm_dp_register_typec_switches);
> >>> +
> >>> +/**
> >>> + * drm_dp_unregister_typec_switches() - unregister Type-C switches
> >>> + * @switch_desc: A Type-C switch descriptor
> >>> + */
> >>> +void drm_dp_unregister_typec_switches(struct drm_dp_typec_switch_desc *switch_desc)
> >>> +{
> >>> +     int i;
> >>> +
> >>> +     for (i = 0; i < switch_desc->num_typec_switches; i++)
> >>> +             typec_mux_unregister(switch_desc->typec_ports[i].typec_mux);
> >>> +}
> >>> +EXPORT_SYMBOL(drm_dp_unregister_typec_switches);
> >>> +#else
> >>> +void drm_dp_unregister_typec_switches(struct drm_dp_typec_switch_desc *switch_desc)
> >>> +{
> >>> +}
> >>> +EXPORT_SYMBOL(drm_dp_register_typec_switches);
> >>> +int drm_dp_register_typec_switches(struct device *dev, struct device_node *port,
> >>> +                                struct drm_dp_typec_switch_desc *switch_desc,
> >>> +                                void *data, typec_mux_set_fn_t mux_set)
> >>> +{
> >>> +     return 0;
> >>> +}
> >>> +EXPORT_SYMBOL(drm_dp_unregister_typec_switches);
> >>> +#endif
> >>> diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
> >>> index ab55453f2d2c..5a3824f13b4e 100644
> >>> --- a/include/drm/display/drm_dp_helper.h
> >>> +++ b/include/drm/display/drm_dp_helper.h
> >>> @@ -25,6 +25,7 @@
> >>>
> >>>    #include <linux/delay.h>
> >>>    #include <linux/i2c.h>
> >>> +#include <linux/usb/typec_mux.h>
> >>>
> >>>    #include <drm/display/drm_dp.h>
> >>>    #include <drm/drm_connector.h>
> >>> @@ -763,4 +764,20 @@ bool drm_dp_downstream_rgb_to_ycbcr_conversion(const u8 dpcd[DP_RECEIVER_CAP_SIZ
> >>>                                               const u8 port_cap[4], u8 color_spc);
> >>>    int drm_dp_pcon_convert_rgb_to_ycbcr(struct drm_dp_aux *aux, u8 color_spc);
> >>>
> >>> +struct drm_dp_typec_port_data {
> >>> +     struct typec_mux_dev *typec_mux;
> >>> +     void *data;
> >>> +     bool dp_connected;
> >>> +};
> >>> +
> >>> +struct drm_dp_typec_switch_desc {
> >>> +     int num_typec_switches;
> >>> +     struct drm_dp_typec_port_data *typec_ports;
> >>> +};
> >>> +
> >>> +void drm_dp_unregister_typec_switches(struct drm_dp_typec_switch_desc *switch_desc);
> >>> +int drm_dp_register_typec_switches(struct device *dev, struct device_node *port,
> >>> +                                struct drm_dp_typec_switch_desc *switch_desc,
> >>> +                                void *data, typec_mux_set_fn_t mux_set);
> >>> +
> >>>    #endif /* _DRM_DP_HELPER_H_ */
> >>
> >> --
> >> With best wishes
> >> Dmitry
> >>
> >
> > Best regards,
> > Pin-yen
>
> --
> With best wishes
> Dmitry
>
Best regards,
Pin-yen