Message-ID: <014959bc-317c-544c-8afe-0e3b56d45e2b@ti.com>
Date:   Tue, 24 Jan 2023 12:10:21 +0530
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Subject: Re: [PATCH v6 3/5] drm/tidss: Add support to configure OLDI mode for
 am625-dss.
To:     Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>,
        Jyri Sarha <jyri.sarha@iki.fi>,
        Rob Herring <robh+dt@kernel.org>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
CC:     DRI Development List <dri-devel@lists.freedesktop.org>,
        Devicetree List <devicetree@vger.kernel.org>,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
        Nishanth Menon <nm@ti.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Rahul T R <r-ravikumar@ti.com>,
        Devarsh Thakkar <devarsht@ti.com>,
        Jayesh Choudhary <j-choudhary@ti.com>
References: <20221119173019.15643-1-a-bhatia1@ti.com>
 <20221119173019.15643-4-a-bhatia1@ti.com>
 <7feda5ce-5cff-3838-94ec-c2a1ef831398@ideasonboard.com>
Content-Language: en-US
From:   Aradhya Bhatia <a-bhatia1@ti.com>
In-Reply-To: <7feda5ce-5cff-3838-94ec-c2a1ef831398@ideasonboard.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
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Precedence: bulk

Hi Tomi,

Thanks for reviewing the patch series. I have implemented the most of
your suggestions, but for the others, I needed to clarify things. I have
made some comments there.

On 20-Dec-22 18:22, Tomi Valkeinen wrote:
> Hi,
> 
> On 19/11/2022 19:30, 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 |
>> |      |        |         |      |       |
>> +------+        +---------+      +-------+
>>
>> 2. OLDI_SINGLE_LINK_CLONE_MODE
>> Duplicate Output over OLDI 0 and 1.
>> +------+        +---------+      +-------+
>> |      |        |         |      |       |
>> | CRTC +---+--->| ENCODER +----->| PANEL |
>> |      |   |    |         |      |       |
>> +------+   |    +---------+      +-------+
>>             |
>>             |    +---------+      +-------+
>>             |    |         |      |       |
>>             +--->| 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 confguring the OLDI modes using OF and LVDS DRM helper
>> functions.
>>
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
>> ---
>>   drivers/gpu/drm/tidss/tidss_dispc.c   |  12 ++
>>   drivers/gpu/drm/tidss/tidss_dispc.h   |   9 ++
>>   drivers/gpu/drm/tidss/tidss_drv.h     |   3 +
>>   drivers/gpu/drm/tidss/tidss_encoder.c |   4 +-
>>   drivers/gpu/drm/tidss/tidss_encoder.h |   3 +-
>>   drivers/gpu/drm/tidss/tidss_kms.c     | 188 +++++++++++++++++++++++---
>>   6 files changed, 198 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c 
>> b/drivers/gpu/drm/tidss/tidss_dispc.c
>> index dbc6a5b617ca..472226a83251 100644
>> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
>> @@ -365,6 +365,8 @@ struct dispc_device {
>>       struct dss_vp_data vp_data[TIDSS_MAX_VPS];
>> +    enum dispc_oldi_modes oldi_mode;
>> +
>>       u32 *fourccs;
>>       u32 num_fourccs;
>> @@ -1967,6 +1969,16 @@ const u32 *dispc_plane_formats(struct 
>> dispc_device *dispc, unsigned int *len)
>>       return dispc->fourccs;
>>   }
>> +int dispc_set_oldi_mode(struct dispc_device *dispc,
>> +            enum dispc_oldi_modes oldi_mode)
>> +{
>> +    WARN_ON(!dispc);
> 
> This feels unnecessary. Is there even a theoretical case where we could 
> get dispc == NULL?
> 
>> +
>> +    dispc->oldi_mode = oldi_mode;
>> +
>> +    return 0;
> 
> This function could as well be void function. >
>> +}
>> +
>>   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 51db500590ee..e76a7599b544 100644
>> --- a/drivers/gpu/drm/tidss/tidss_dispc.h
>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.h
>> @@ -64,6 +64,14 @@ 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. */
>> +    OLDI_MODE_UNSUPPORTED,        /* Unsupported OLDI Mode */
>> +};
> 
> What is the difference with MODE_OFF and MODE_UNSUPPORTED? Is 
> MODE_UNSUPPORTED for cases where, e.g., the DT setup is wrong and the 
> driver should return an error? The code doesn't quite do that, it prints 
> an error but then continues.

Yes, OLDI_MODE_UNSUPPORTED is for the cases where DT setup is wrong.
I have not exited in such a cases with an error, because then the driver
will never have a chance to setup the 2nd pipeline (DPI) even if all the
DT requirements are met.

> 
>>   struct dispc_features {
>>       int min_pclk_khz;
>>       int max_pclk_khz[DISPC_VP_MAX_BUS_TYPE];
>> @@ -133,6 +141,7 @@ 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_set_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 0ce7ee5ccd5b..58892f065c16 100644
>> --- a/drivers/gpu/drm/tidss/tidss_drv.h
>> +++ b/drivers/gpu/drm/tidss/tidss_drv.h
>> @@ -13,6 +13,9 @@
>>   #define TIDSS_MAX_PLANES 4
>>   #define TIDSS_MAX_OUTPUT_PORTS 4
>> +/* For AM625-DSS with 2 OLDI TXes */
>> +#define TIDSS_MAX_BRIDGES_PER_PIPE    2
>> +
>>   typedef u32 dispc_irq_t;
>>   struct tidss_device {
>> diff --git a/drivers/gpu/drm/tidss/tidss_encoder.c 
>> b/drivers/gpu/drm/tidss/tidss_encoder.c
>> index e278a9c89476..141383ec4045 100644
>> --- a/drivers/gpu/drm/tidss/tidss_encoder.c
>> +++ b/drivers/gpu/drm/tidss/tidss_encoder.c
>> @@ -70,7 +70,8 @@ static const struct drm_encoder_funcs encoder_funcs = {
>>   };
>>   struct drm_encoder *tidss_encoder_create(struct tidss_device *tidss,
>> -                     u32 encoder_type, u32 possible_crtcs)
>> +                     u32 encoder_type, u32 possible_crtcs,
>> +                     u32 possible_clones)
>>   {
>>       struct drm_encoder *enc;
>>       int ret;
>> @@ -80,6 +81,7 @@ struct drm_encoder *tidss_encoder_create(struct 
>> tidss_device *tidss,
>>           return ERR_PTR(-ENOMEM);
>>       enc->possible_crtcs = possible_crtcs;
>> +    enc->possible_clones = possible_clones;
>>       ret = drm_encoder_init(&tidss->ddev, enc, &encoder_funcs,
>>                      encoder_type, NULL);
>> diff --git a/drivers/gpu/drm/tidss/tidss_encoder.h 
>> b/drivers/gpu/drm/tidss/tidss_encoder.h
>> index ace877c0e0fd..01c62ba3ef16 100644
>> --- a/drivers/gpu/drm/tidss/tidss_encoder.h
>> +++ b/drivers/gpu/drm/tidss/tidss_encoder.h
>> @@ -12,6 +12,7 @@
>>   struct tidss_device;
>>   struct drm_encoder *tidss_encoder_create(struct tidss_device *tidss,
>> -                     u32 encoder_type, u32 possible_crtcs);
>> +                     u32 encoder_type, u32 possible_crtcs,
>> +                     u32 possible_clones);
>>   #endif
>> diff --git a/drivers/gpu/drm/tidss/tidss_kms.c 
>> b/drivers/gpu/drm/tidss/tidss_kms.c
>> index fc9c4eefd31d..8ae321f02197 100644
>> --- a/drivers/gpu/drm/tidss/tidss_kms.c
>> +++ b/drivers/gpu/drm/tidss/tidss_kms.c
>> @@ -106,30 +106,115 @@ static const struct drm_mode_config_funcs 
>> mode_config_funcs = {
>>       .atomic_commit = drm_atomic_helper_commit,
>>   };
>> +static enum dispc_oldi_modes tidss_get_oldi_mode(struct device_node 
>> *oldi0_port,
>> +                         struct device_node *oldi1_port)
>> +{
>> +    int pixel_order;
>> +
>> +    if (!(oldi0_port || oldi1_port)) {
>> +        /* Keep OLDI TXes off if neither OLDI port is present. */
>> +        return OLDI_MODE_OFF;
>> +    } else if (oldi0_port && !oldi1_port) {
>> +        /*
>> +         * OLDI0 port found, but not OLDI1 port. Setting single
>> +         * link, single mode output.
>> +         */
>> +        return OLDI_SINGLE_LINK_SINGLE_MODE;
>> +    } else if (!oldi0_port && oldi1_port) {
>> +        /*
>> +         * The 2nd OLDI TX cannot be operated alone. This use case is
>> +         * not supported in the HW. Since the pins for OLDIs 0 and 1 are
>> +         * separate, one could theoretically set a clone mode over OLDIs
>> +         * 0 and 1 and just simply not use the OLDI 0. This is a hacky
>> +         * way to enable only OLDI TX 1 and hence is not officially
>> +         * supported.
>> +         */
>> +        return OLDI_MODE_UNSUPPORTED;
> 
> If OLDI_MODE_UNSUPPORTED is supposed to result in an error, maybe you 
> could print the error here (and possibly in the default case below), and 
> then, in the caller, just return with an error code.
> 
>> +    }
>> +
>> +    /*
>> +     * 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:
>> +        /*
>> +         * 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.
>> +         */
>> +        pr_warn("EVEN-ODD config for dual-link sinks is not supported in HW. Switching to ODD-EVEN.\n");
> 
> Please use dev_warn() instead, so that it will be clear where the print 
> comes from.
> 
> In any case, isn't this an error? Do you really want to accept the wrong 
> pixel order?
> 
>> +        fallthrough;
>> +
>> +    case DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS:
>> +        return OLDI_DUAL_LINK_MODE;
>> +
>> +    default:
>> +        return OLDI_MODE_OFF;
> 
> When do we get here? Shouldn't this be OLDI_MODE_UNSUPPORTED?
> 
>> +    }
>> +}
>> +
>>   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_BRIDGES_PER_PIPE];
>>           u32 enc_type;
>> +        u32 num_bridges;
>>       };
>>       const struct dispc_features *feat = tidss->feat;
>> -    u32 max_vps = feat->num_vps;
>> +    u32 output_ports = feat->num_output_ports;
>>       u32 max_planes = feat->num_planes;
>> -    struct pipe pipes[TIDSS_MAX_VPS];
>> +    struct pipe pipes[TIDSS_MAX_VPS] = {0};
>> +
>>       u32 num_pipes = 0;
>>       u32 crtc_mask;
>> +    u32 portnum_oldi0 = 0, portnum_oldi1 = 2;
> 
> These two are bit of hacks. First, they should be const, or maybe 
> defines. If they're const, they can be inside the block below.
> 
> And they're very much tied to the HW in question, so just having 
> hardcoded values here inside a function without any mention of the 
> situation is not good.
> 
> Doing this in a generic and future proof manner is... challenging. So I 
> think using the hardcoded port numbers is fine. But they are only ok for 
> the two AM6xx SoCs we have now so the 'oldi_supported' is not very good 
> fit. In fact, it might be good to drop 'oldi_supported' altogether, and 
> just check for the SoC versions instead, as (with a quick glance), all 
> the 'oldi_supported' checks are really SoC specific.
> 
I will be make these portnum variables const as you suggested and
moving these as well as get-node and put-node function calls to the
get_oldi_mode function to keep things clear.

However, I believe the 'oldi_supported' variable should still be kept
(after renaming it to has_oldi as per your suggestion in the previous
patch) because having this variable will help distinguish from the cases
where an SoC *can* support OLDI output but its output by-passes the OLDI
TXes and a DPI output is expected.

> This also again brings up a thing that rubs me the wrong way: the new 
> OLDI port is port 2. I really think that on AM62x, the two OLDI ports 
> should be 0 and 1, and the DPI should be 2. Would we need a new 
> dt-binding doc for that, or could it still be described in the same doc? 
> Would that change cause changes elsewhere in the dss driver?
> 
>> +    enum dispc_oldi_modes oldi_mode = OLDI_MODE_OFF;
>> +    u32 num_oldi = 0;
>> +    u32 oldi_pipe_index = 0;
>> +    u32 num_encoders = 0;
>> +
>> +    if (feat->oldi_supported) {
>> +        struct device_node *oldi0_port, *oldi1_port;
>> +
>> +        oldi0_port = of_graph_get_port_by_id(dev->of_node,
>> +                             portnum_oldi0);
>> +        oldi1_port = of_graph_get_port_by_id(dev->of_node,
>> +                             portnum_oldi1);
>> +
>> +        oldi_mode = tidss_get_oldi_mode(oldi0_port, oldi1_port);
>> +
>> +        of_node_put(oldi0_port);
>> +        of_node_put(oldi1_port);
>> +
>> +        dispc_set_oldi_mode(tidss->dispc, oldi_mode);
>> +    }
>>       /* first find all the connected panels & bridges */
>> -    for (i = 0; i < max_vps; i++) {
>> +    for (i = 0; i < output_ports; i++) {
>>           struct drm_panel *panel;
>>           struct drm_bridge *bridge;
>>           u32 enc_type = DRM_MODE_ENCODER_NONE;
>> @@ -145,16 +230,24 @@ static int tidss_dispc_modeset_init(struct 
>> tidss_device *tidss)
>>               return ret;
>>           }
>> +        if (feat->output_port_bus_type[i] == DISPC_VP_OLDI &&
>> +            oldi_mode == OLDI_MODE_UNSUPPORTED) {
>> +            dev_err(dev,
>> +                "Single Mode over OLDI 1 is not supported in HW. Keeping OLDI off.\n");
>> +            continue;
> 
> Should we error out here?
> 
>> +        }
>> +
>>           if (panel) {
>>               u32 conn_type;
>>               dev_dbg(dev, "Setting up panel for port %d\n", i);
>> -            switch (feat->vp_bus_type[i]) {
>> +            switch (feat->output_port_bus_type[i]) {
>>               case DISPC_VP_OLDI:
>>                   enc_type = DRM_MODE_ENCODER_LVDS;
>>                   conn_type = DRM_MODE_CONNECTOR_LVDS;
>>                   break;
>> +
>>               case DISPC_VP_DPI:
>>                   enc_type = DRM_MODE_ENCODER_DPI;
>>                   conn_type = DRM_MODE_CONNECTOR_DPI;
>> @@ -172,6 +265,17 @@ static int tidss_dispc_modeset_init(struct 
>> tidss_device *tidss)
>>                   return -EINVAL;
>>               }
>> +            /*
>> +             * If the 2nd OLDI port is discovered connected to a panel
>> +             * which is not to be connected in the Clone Mode then a
>> +             * bridge is not required because the detected port is the
>> +             * 2nd port for the previously connected panel.
>> +             */
>> +            if (feat->output_port_bus_type[i] == DISPC_VP_OLDI &&
>> +                oldi_mode != OLDI_SINGLE_LINK_CLONE_MODE &&
> 
  > Hmm, shouldn't this be oldi_mode == OLDI_DUAL_LINK_MODE? Or rather,
Yes. I will make the change...

> shouldn't we test here if this is the second oldi display, and if so 
> which oldi-mode are we using. If dual-link, break. If clone, continue. 
> Otherwise, error.
but, if I implement the oldi-mode-find logic over here, that would be
limited to panels and will skip out the bridges. And the mode-find
should really be only done once.

That said, I see that this can get a little confusing, So, while keeping
the mode-find logic separate, I have organized the other OLDI specific
things separately in the next patch.

> 
>> +                num_oldi)
>> +                break;
>> +
>>               bridge = devm_drm_panel_bridge_add(dev, panel);
>>               if (IS_ERR(bridge)) {
>>                   dev_err(dev,
>> @@ -181,10 +285,47 @@ static int tidss_dispc_modeset_init(struct 
>> tidss_device *tidss)
>>               }
>>           }
>> -        pipes[num_pipes].hw_videoport = i;
>> -        pipes[num_pipes].bridge = bridge;
>> -        pipes[num_pipes].enc_type = enc_type;
>> -        num_pipes++;
>> +        if (feat->output_port_bus_type[i] == DISPC_VP_OLDI) {
>> +            if (++num_oldi == 1) {
>> +                /* Setting up pipe parameters when 1st OLDI port is detected */
>> +
>> +                pipes[num_pipes].hw_videoport = i;
>> +                pipes[num_pipes].enc_type = enc_type;
>> +
>> +                /*
>> +                 * Saving the pipe index in case its required for
>> +                 * 2nd OLDI Port.
>> +                 */
>> +                oldi_pipe_index = num_pipes;
>> +
>> +                /*
>> +                 * No additional pipe is required for the 2nd OLDI
>> +                 * port, because the 2nd Encoder -> Bridge connection
>> +                 * is the part of the first OLDI Port pipe.
>> +                 *
>> +                 * num_pipes will only be incremented when the first
>> +                 * OLDI port is discovered.
>> +                 */
>> +                num_pipes++;
>> +            }
>> +
>> +            /*
>> +             * Bridge is required to be added only if the detected
>> +             * port is the first OLDI port or a subsequent port in
>> +             * Clone Mode.
>> +             */
>> +            if (oldi_mode == OLDI_SINGLE_LINK_CLONE_MODE ||
>> +                num_oldi == 1) {
>> +                pipes[oldi_pipe_index].bridge[num_oldi - 1] = bridge;
>> +                pipes[oldi_pipe_index].num_bridges++;
>> +            }
>> +        } else {
>> +            pipes[num_pipes].hw_videoport = i;
>> +            pipes[num_pipes].bridge[0] = bridge;
>> +            pipes[num_pipes].num_bridges++;
>> +            pipes[num_pipes].enc_type = enc_type;
>> +            num_pipes++;
>> +        }
>>       }
>>       /* all planes can be on any crtc */
>> @@ -196,6 +337,7 @@ static int tidss_dispc_modeset_init(struct 
>> tidss_device *tidss)
>>           struct tidss_plane *tplane;
>>           struct tidss_crtc *tcrtc;
>>           struct drm_encoder *enc;
>> +        u32 possible_clones = 0;
>>           u32 hw_plane_id = feat->vid_order[tidss->num_planes];
>>           int ret;
>> @@ -218,16 +360,24 @@ static int tidss_dispc_modeset_init(struct 
>> tidss_device *tidss)
>>           tidss->crtcs[tidss->num_crtcs++] = &tcrtc->crtc;
>> -        enc = tidss_encoder_create(tidss, pipes[i].enc_type,
>> -                       1 << tcrtc->crtc.index);
>> -        if (IS_ERR(enc)) {
>> -            dev_err(tidss->dev, "encoder create failed\n");
>> -            return PTR_ERR(enc);
>> -        }
>> +        for (j = 0; j < pipes[i].num_bridges; j++) {
>> +            if (pipes[i].num_bridges > 1)
>> +                possible_clones = (((1 << pipes[i].num_bridges) - 1)
>> +                          << num_encoders);
> 
> I think the above possible_clones assignment can be outside the for loop. >
>> +
>> +            enc = tidss_encoder_create(tidss, pipes[i].enc_type,
>> +                           1 << tcrtc->crtc.index,
>> +                           possible_clones);
>> +            if (IS_ERR(enc)) {
>> +                dev_err(tidss->dev, "encoder create failed\n");
>> +                return PTR_ERR(enc);
>> +            }
>> -        ret = drm_bridge_attach(enc, pipes[i].bridge, NULL, 0);
>> -        if (ret)
>> -            return ret;
>> +            ret = drm_bridge_attach(enc, pipes[i].bridge[j], NULL, 0);
>> +            if (ret)
>> +                return ret;
>> +        }
>> +        num_encoders += pipes[i].num_bridges;
>>       }
>>       /* create overlay planes of the leftover planes */

Regards
Aradhya