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Date:   Thu, 12 Jan 2023 07:24:50 +0200
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Subject: Re: [PATCH v10 3/9] drm/display: Add Type-C switch helpers
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To:     Pin-yen Lin <treapking@chromium.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?Q?N=c3=adcolas_F_=2e_R_=2e_A_=2e_Prado?= 
        <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>
References: <20230112042104.4107253-1-treapking@chromium.org>
 <20230112042104.4107253-4-treapking@chromium.org>
 <ccea730e-c5cb-4225-8d1e-97a0a7cb2e34@linaro.org>
 <CAEXTbpek=5xqo2j0yKkC90+Oy1rXWQLJWu3X6vx6y-SqvxTvnA@mail.gmail.com>
From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
In-Reply-To: <CAEXTbpek=5xqo2j0yKkC90+Oy1rXWQLJWu3X6vx6y-SqvxTvnA@mail.gmail.com>
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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).

>>
>>> +     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