Message-ID: <61e67300-3ed4-827f-34c6-9317fef69673@ideasonboard.com>
Date:   Mon, 24 Oct 2022 10:17:03 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Aradhya Bhatia <a-bhatia1@...com>, Jyri Sarha <jyri.sarha@....fi>,
        Rob Herring <robh+dt@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Rahul T R <r-ravikumar@...com>,
        DRI Development List <dri-devel@...ts.freedesktop.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 4/6] drm/tidss: Add support to configure OLDI mode
 for am625-dss.

On 18/10/2022 10:00, Aradhya Bhatia wrote:
> Hi Tomi
> 
> Thank you for the comprehensive feedback across all the patches. I am
> working on them.
> 
> I do have some concerns which I have talked about, below.
> 
> On 12-Oct-22 17:53, Tomi Valkeinen wrote:
>> On 28/09/2022 20:52, Aradhya Bhatia wrote:
>>> The newer version of DSS (AM625-DSS) has 2 OLDI TXes at its disposal.
>>> These can be configured to support the following modes:
>>>
>>> 1. OLDI_SINGLE_LINK_SINGLE_MODE
>>> Single Output over OLDI 0.
>>> +------+        +---------+      +-------+
>>> |      |        |         |      |       |
>>> | CRTC +------->+ ENCODER +----->| PANEL |
>>> |      |        |         |      |       |
>>> +------+        +---------+      +-------+
>>
>> Can you have single link on OLDI 1 (OLDI 0 off)? I don't know if that 
>> make sense on this platform, but if the pins for OLDI 0 and 1 are 
>> different, there might be a reason on some cases for that.
> 
> HW does not support a case where single link is enabled over OLDI 1 with
> OLDI 0 off, even though the pins are different.
> 
> One could still put 2 panel nodes in DT to set OLDI in a Clone Mode and
> simply not use OLDI 0 pins, but I dont think that is a valid case that
> should be supported.
> 
>>
>>> 2. OLDI_SINGLE_LINK_CLONE_MODE
>>> Duplicate Output over OLDI 0 and 1.
>>> +------+        +---------+      +-------+
>>> |      |        |         |      |       |
>>> | CRTC +---+--->| ENCODER +----->| PANEL |
>>> |      |   |    |         |      |       |
>>> +------+   |    +---------+      +-------+
>>>        |
>>
>> I think you've got a tab in the line above, but otherwise use spaces.
>>
>>>             |    +---------+      +-------+
>>>             |    |         |      |       |
>>>             +--->| ENCODER +----->| PANEL |
>>>                  |         |      |       |
>>>                  +---------+      +-------+
>>>
>>> 3. OLDI_DUAL_LINK_MODE
>>> Combined Output over OLDI 0 and 1.
>>> +------+        +---------+      +-------+
>>> |      |        |         +----->|       |
>>> | CRTC +------->+ ENCODER |      | PANEL |
>>> |      |        |         +----->|       |
>>> +------+        +---------+      +-------+
>>>
>>> Following the above pathways for different modes, 2 encoder/panel-bridge
>>> pipes get created for clone mode, and 1 pipe in cases of single link and
>>> dual link mode.
>>>
>>> Add support for confgure the OLDI modes using of and lvds DRM helper
>>
>> "configuring"
>>
>>> functions.
>>>
>>> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
>>> ---
>>>   drivers/gpu/drm/tidss/tidss_dispc.c |  11 +++
>>>   drivers/gpu/drm/tidss/tidss_dispc.h |   8 ++
>>>   drivers/gpu/drm/tidss/tidss_drv.h   |   3 +
>>>   drivers/gpu/drm/tidss/tidss_kms.c   | 146 +++++++++++++++++++++++-----
>>>   4 files changed, 145 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c 
>>> b/drivers/gpu/drm/tidss/tidss_dispc.c
>>> index 34f0da4bb3e3..88008ad39b55 100644
>>> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
>>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
>>> @@ -354,6 +354,8 @@ struct dispc_device {
>>>       bool is_enabled;
>>> +    enum dispc_oldi_modes oldi_mode;
>>> +
>>>       struct dss_vp_data vp_data[TIDSS_MAX_PORTS];
>>>       u32 *fourccs;
>>> @@ -1958,6 +1960,15 @@ const u32 *dispc_plane_formats(struct 
>>> dispc_device *dispc, unsigned int *len)
>>>       return dispc->fourccs;
>>>   }
>>> +int dispc_configure_oldi_mode(struct dispc_device *dispc,
>>> +                  enum dispc_oldi_modes oldi_mode)
>>> +{
>>> +    WARN_ON(!dispc);
>>> +
>>> +    dispc->oldi_mode = oldi_mode;
>>> +    return 0;
>>> +}
>>
>> I think "configure" means more than just storing the value. Maybe 
>> dispc_set_oldi_mode(). And an empty line above the return.
>>
>>> +
>>>   static s32 pixinc(int pixels, u8 ps)
>>>   {
>>>       if (pixels == 1)
>>> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.h 
>>> b/drivers/gpu/drm/tidss/tidss_dispc.h
>>> index b66418e583ee..45cce1054832 100644
>>> --- a/drivers/gpu/drm/tidss/tidss_dispc.h
>>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.h
>>> @@ -64,6 +64,13 @@ enum dispc_dss_subrevision {
>>>       DISPC_AM625,
>>>   };
>>> +enum dispc_oldi_modes {
>>> +    OLDI_MODE_OFF,                /* OLDI turned off / tied off in 
>>> IP. */
>>> +    OLDI_SINGLE_LINK_SINGLE_MODE,        /* Single Output over OLDI 
>>> 0. */
>>> +    OLDI_SINGLE_LINK_CLONE_MODE,        /* Duplicate Output over 
>>> OLDI 0 and 1. */
>>> +    OLDI_DUAL_LINK_MODE,            /* Combined Output over OLDI 0 
>>> and 1. */
>>> +};
>>> +
>>>   struct dispc_features {
>>>       int min_pclk_khz;
>>>       int max_pclk_khz[DISPC_VP_MAX_BUS_TYPE];
>>> @@ -131,6 +138,7 @@ int dispc_plane_setup(struct dispc_device *dispc, 
>>> u32 hw_plane,
>>>                 u32 hw_videoport);
>>>   int dispc_plane_enable(struct dispc_device *dispc, u32 hw_plane, 
>>> bool enable);
>>>   const u32 *dispc_plane_formats(struct dispc_device *dispc, unsigned 
>>> int *len);
>>> +int dispc_configure_oldi_mode(struct dispc_device *dispc, enum 
>>> dispc_oldi_modes oldi_mode);
>>>   int dispc_init(struct tidss_device *tidss);
>>>   void dispc_remove(struct tidss_device *tidss);
>>> diff --git a/drivers/gpu/drm/tidss/tidss_drv.h 
>>> b/drivers/gpu/drm/tidss/tidss_drv.h
>>> index d7f27b0b0315..2252ba0222ca 100644
>>> --- a/drivers/gpu/drm/tidss/tidss_drv.h
>>> +++ b/drivers/gpu/drm/tidss/tidss_drv.h
>>> @@ -12,6 +12,9 @@
>>>   #define TIDSS_MAX_PORTS 4
>>>   #define TIDSS_MAX_PLANES 4
>>> +/* For AM625-DSS with 2 OLDI TXes */
>>> +#define TIDSS_MAX_BRIDGE_PER_PIPE    2
>>
>> "BRIDGES"?
>>
>>> +
>>>   typedef u32 dispc_irq_t;
>>>   struct tidss_device {
>>> diff --git a/drivers/gpu/drm/tidss/tidss_kms.c 
>>> b/drivers/gpu/drm/tidss/tidss_kms.c
>>> index 666e527a0acf..73afe390f36d 100644
>>> --- a/drivers/gpu/drm/tidss/tidss_kms.c
>>> +++ b/drivers/gpu/drm/tidss/tidss_kms.c
>>> @@ -107,32 +107,84 @@ static const struct drm_mode_config_funcs 
>>> mode_config_funcs = {
>>>       .atomic_commit = drm_atomic_helper_commit,
>>>   };
>>> +static int tidss_get_oldi_mode(struct tidss_device *tidss)
>>
>> Return enum dispc_oldi_modes, not int.
>>
>>> +{
>>> +    int pixel_order;
>>> +    struct device_node *dss_ports, *oldi0_port, *oldi1_port;
>>> +
>>> +    dss_ports = of_get_next_child(tidss->dev->of_node, NULL);
>>
>> Hmm you get the next child and hope that it's the ports node?
>>
>> In any case, I think you can call of_graph_get_port_by_id() with the 
>> tidss->dev->of_node and it'll do the right thing.
> I think this will only work if the child of dss node is just "ports",
> but we've been using "dss_ports" as the child.
> 
> However, you are right. I shouldn't expect the first child to be
> dss_ports. I will use the "of_get_child_by_name" helper to get the
> dss_ports node.

I don't think you need to. of_graph_get_port_by_id() should work fine 
with the dss node.

>>> +    oldi0_port = of_graph_get_port_by_id(dss_ports, 0);
>>> +    oldi1_port = of_graph_get_port_by_id(dss_ports, 2);
>>
>> I think you need to of_put these at some point.
>>
>>> +    if (!(oldi0_port && oldi1_port))
>>> +        return OLDI_SINGLE_LINK_SINGLE_MODE;
>>
>> This one matches also for !oldi0 && oldi1. If oldi1 cannot be used in 
>> single-link mode, the above should take it into account.
> 
> Right. I will print a warning if somebody's trying to use (!oldi0 &&
> oldi1) but since its a single link requirement, I will still set the
> OLDI for single link single mode.
> 
>>
>>> +
>>> +    /*
>>> +     * OLDI Ports found for both the OLDI TXes. The DSS is to be 
>>> configured
>>> +     * in either Dual Link or Clone Mode.
>>> +     */
>>> +    pixel_order = drm_of_lvds_get_dual_link_pixel_order(oldi0_port,
>>> +                                oldi1_port);
>>> +    switch (pixel_order) {
>>> +    case -EINVAL:
>>> +        /*
>>> +         * The dual link properties were not found in at least one of
>>> +         * the sink nodes. Since 2 OLDI ports are present in the DT, it
>>> +         * can be safely assumed that the required configuration is
>>> +         * Clone Mode.
>>> +         */
>>> +        return OLDI_SINGLE_LINK_CLONE_MODE;
>>> +
>>> +    case DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS:
>>> +    case DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS:
>>> +        /*
>>> +         * Note that the OLDI TX 0 transmits the odd set of pixels 
>>> while
>>> +         * the OLDI TX 1 transmits the even set. This is a fixed
>>> +         * configuration in the IP and an cannot be change vis SW. 
>>> These
>>> +         * properties have been used to merely identify if a Dual Link
>>> +         * configuration is required. Swapping this property in the 
>>> panel
>>> +         * port DT nodes will not make any difference.
>>> +         */
>>
>> But if they are in the wrong order, shouldn't we fail or at least give 
>> a warning?
>>  >> +        return OLDI_DUAL_LINK_MODE;
>>> +
>>> +    default:
>>> +        return OLDI_MODE_OFF;
>>> +    }
>>> +}
>>> +
>>>   static int tidss_dispc_modeset_init(struct tidss_device *tidss)
>>>   {
>>>       struct device *dev = tidss->dev;
>>>       unsigned int fourccs_len;
>>>       const u32 *fourccs = dispc_plane_formats(tidss->dispc, 
>>> &fourccs_len);
>>> -    unsigned int i;
>>> +    unsigned int i, j;
>>>       struct pipe {
>>>           u32 hw_videoport;
>>> -        struct drm_bridge *bridge;
>>> +        struct drm_bridge *bridge[TIDSS_MAX_BRIDGE_PER_PIPE];
>>>           u32 enc_type;
>>> +        u32 num_bridges;
>>>       };
>>>       const struct dispc_features *feat = tidss->feat;
>>> -    u32 max_vps = feat->num_vps;
>>> +    u32 max_ports = feat->num_max_ports;
>>>       u32 max_planes = feat->num_planes;
>>>       struct pipe pipes[TIDSS_MAX_PORTS];
>>>       u32 num_pipes = 0;
>>> +    u32 pipe_number = 0;
>>>       u32 crtc_mask;
>>> +    u32 num_oldi = 0;
>>> +    u32 oldi0_port = 0;
>>> +    u32 hw_vp = 0;
>>> +    enum dispc_oldi_modes oldi_mode;
>>>       /* first find all the connected panels & bridges */
>>> -    for (i = 0; i < max_vps; i++) {
>>> +    for (i = 0; i < max_ports; i++) {
>>>           struct drm_panel *panel;
>>>           struct drm_bridge *bridge;
>>> +        bool bridge_req = true;
>>>           u32 enc_type = DRM_MODE_ENCODER_NONE;
>>>           int ret;
>>> @@ -146,6 +198,11 @@ static int tidss_dispc_modeset_init(struct 
>>> tidss_device *tidss)
>>>               return ret;
>>>           }
>>> +        /* default number of bridges required for a panel/bridge*/
>>> +        pipe_number = num_pipes;
>>> +        pipes[pipe_number].num_bridges = 1;
>>> +        hw_vp = i;
>>> +
>>>           if (panel) {
>>>               u32 conn_type;
>>> @@ -155,7 +212,43 @@ static int tidss_dispc_modeset_init(struct 
>>> tidss_device *tidss)
>>>               case DISPC_VP_OLDI:
>>>                   enc_type = DRM_MODE_ENCODER_LVDS;
>>>                   conn_type = DRM_MODE_CONNECTOR_LVDS;
>>> +
>>> +                /*
>>> +                 * A single DSS controller cannot support 2
>>> +                 * independent displays. If 2nd node is detected,
>>> +                 * it is for Dual Link Mode or Clone Mode.
>>> +                 *
>>> +                 * A new pipe instance is not required.
>>> +                 */
>>> +                if (++num_oldi == 2) {
>>> +                    pipe_number = oldi0_port;
>>> +                    hw_vp = i;
>>> +
>>> +                    /* 2nd OLDI DT node detected. Get its mode */
>>> +                    oldi_mode = tidss_get_oldi_mode(tidss);
>>> +                    bridge_req = false;
>>> +
>>> +                    /*
>>> +                     * A separate panel bridge will only be
>>> +                     * required if 2 panels are connected for
>>> +                     * the OLDI Clone Mode.
>>> +                     */
>>> +                    if (oldi_mode == OLDI_SINGLE_LINK_CLONE_MODE) {
>>> +                        bridge_req = true;
>>> +                        (pipes[pipe_number].num_bridges)++;
>>> +                    }
>>> +                } else {
>>> +                    /*
>>> +                     * First OLDI DT node detected. Save it
>>> +                     * in case there is another node for Dual
>>> +                     * Link Mode or Clone Mode.
>>> +                     */
>>> +                    oldi0_port = i;
>>> +                    oldi_mode = OLDI_SINGLE_LINK_SINGLE_MODE;
>>> +                }
>>> +                dispc_configure_oldi_mode(tidss->dispc, oldi_mode);
>>>                   break;
>>> +
>>>               case DISPC_VP_DPI:
>>>                   enc_type = DRM_MODE_ENCODER_DPI;
>>>                   conn_type = DRM_MODE_CONNECTOR_DPI;
>>> @@ -173,19 +266,23 @@ static int tidss_dispc_modeset_init(struct 
>>> tidss_device *tidss)
>>>                   return -EINVAL;
>>>               }
>>> -            bridge = devm_drm_panel_bridge_add(dev, panel);
>>> -            if (IS_ERR(bridge)) {
>>> -                dev_err(dev,
>>> -                    "failed to set up panel bridge for port %d\n",
>>> -                    i);
>>> -                return PTR_ERR(bridge);
>>> +            if (bridge_req) {
>>> +                bridge = devm_drm_panel_bridge_add(dev, panel);
>>> +                if (IS_ERR(bridge)) {
>>> +                    dev_err(dev,
>>> +                        "failed to set up panel bridge for port %d\n",
>>> +                        i);
>>> +                    return PTR_ERR(bridge);
>>> +                }
>>>               }
>>>           }
>>> -        pipes[num_pipes].hw_videoport = i;
>>> -        pipes[num_pipes].bridge = bridge;
>>> -        pipes[num_pipes].enc_type = enc_type;
>>> -        num_pipes++;
>>> +        if (bridge_req) {
>>> +            pipes[pipe_number].hw_videoport = hw_vp;
>>> +            pipes[pipe_number].bridge[pipes[pipe_number].num_bridges 
>>> - 1] = bridge;
>>> +            pipes[pipe_number].enc_type = enc_type;
>>> +            num_pipes++;
>>> +        }
>>
>> I need to look at this with better time. But I started to wonder, 
>> would it be clearer to first figure out the oldi setup before the 
>> loop, rather than figuring it out inside the loop. I'm not sure if it 
>> would help much, though.
>>
> I had not thought about taking this approach, but it might actually be
> better.
> 
> These patches, at the moment, do not support a case where a clone mode
> or dual link mode is used on a bridge instead of a panel. My edits
> inside the loop are panel dependent. If we do have oldi setup
> information prior to the beginning of the loop, the panel dependency can
> be removed and some commond code can be written to support an additional
> encoder - bridge connection should it be required.
> 
> Let me know what you think!
> 
> If this apparch is better indeed, I will make these changes before
> sending out the next revision.

I'll say if it's better when I see the code =). But generally speaking, 
I think it's often better to first figure out what is needed and only 
after that do the actual work. Especially in probe-time code where it's 
not a big deal if you iterate over the ports multiple times, instead of 
doing all in a single loop.

  Tomi

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