Message-ID: <94cf519a-a72f-89d8-fe2a-9fa795ede6ac@ti.com>
Date:   Sun, 5 Feb 2023 18:38:28 +0530
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Subject: Re: [PATCH v7 1/6] drm/tidss: Remove Video Port to Output Port
 coupling
Content-Language: en-US
To:     Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Jyri Sarha <jyri.sarha@iki.fi>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>
CC:     Nishanth Menon <nm@ti.com>,
        Devicetree List <devicetree@vger.kernel.org>,
        Jayesh Choudhary <j-choudhary@ti.com>,
        Jai Luthra <j-luthra@ti.com>, Rahul T R <r-ravikumar@ti.com>,
        Devarsh Thakkar <devarsht@ti.com>,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
        DRI Development List <dri-devel@lists.freedesktop.org>,
        Vignesh Raghavendra <vigneshr@ti.com>
References: <20230125113529.13952-1-a-bhatia1@ti.com>
 <20230125113529.13952-2-a-bhatia1@ti.com>
 <300c0351-6ee0-d703-bd53-bc4c0fe3af0f@ideasonboard.com>
From:   Aradhya Bhatia <a-bhatia1@ti.com>
In-Reply-To: <300c0351-6ee0-d703-bd53-bc4c0fe3af0f@ideasonboard.com>
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Hi Tomi,

Thanks for the review!

On 03-Feb-23 16:53, Tomi Valkeinen wrote:
> On 25/01/2023 13:35, Aradhya Bhatia wrote:
>> Make DSS Video Ports agnostic of output bus types.
>>
>> DSS controllers have had a 1-to-1 coupling between its VPs and its
>> output ports. This no longer stands true for the new AM625 DSS. This
>> coupling, hence, has been removed by renaming the 'vp_bus_type' to
>> 'output_port_bus_type' because the VPs are essentially agnostic of the
>> bus type and it is the output ports which have a bus type.
>>
>> The AM625 DSS has 2 VPs but requires 3 output ports to support its
>> Dual-Link OLDI video output coming from a single VP.
> 
> Not a biggie, but this sentence is a bit odd here at the end. Shouldn't
> it be after the "...stands true for the new AM625 DSS."?

Yes! It should be. Will make the edit.

> 
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
>> ---
>>   drivers/gpu/drm/tidss/tidss_dispc.c | 47 +++++++++++++++++------------
>>   drivers/gpu/drm/tidss/tidss_dispc.h | 21 +++++++------
>>   drivers/gpu/drm/tidss/tidss_drv.h   |  5 +--
>>   drivers/gpu/drm/tidss/tidss_irq.h   |  2 +-
>>   drivers/gpu/drm/tidss/tidss_kms.c   | 12 ++++----
>>   5 files changed, 48 insertions(+), 39 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
>> index 165365b515e1..c1c4faccbddc 100644
>> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
>> @@ -61,7 +61,7 @@ const struct dispc_features dispc_k2g_feats = {
>>       .min_pclk_khz = 4375,
>>         .max_pclk_khz = {
>> -        [DISPC_VP_DPI] = 150000,
>> +        [DISPC_PORT_DPI] = 150000,
>>       },
>>         /*
>> @@ -96,7 +96,6 @@ const struct dispc_features dispc_k2g_feats = {
>>       .vp_name = { "vp1" },
>>       .ovr_name = { "ovr1" },
>>       .vpclk_name =  { "vp1" },
>> -    .vp_bus_type = { DISPC_VP_DPI },
>>         .vp_feat = { .color = {
>>               .has_ctm = true,
>> @@ -109,6 +108,9 @@ const struct dispc_features dispc_k2g_feats = {
>>       .vid_name = { "vid1" },
>>       .vid_lite = { false },
>>       .vid_order = { 0 },
>> +
>> +    .num_output_ports = 1,
>> +    .output_port_bus_type = { DISPC_PORT_DPI },
>>   };
> 
> Just thinking out loud, as these will get more complex in the future,
> maybe we should finally group them with struct. E.g. we could define
> struct array for vps, like (just hacky example):
> 
>     struct {
>         const char *name;
>         const char *clkname;
>         struct tidss_vp_feat feat;
>     } vps[TIDSS_MAX_PORTS];
> 
> and then use them as:
> 
>     .vps = {
>         {
>             .name = "kala",
>             .clkname = "kissa",
>             .feat.color.has_ctm = true,
>         }, {
>             .name = "kala2",
>             .clkname = "kissa2",
>             .feat.color.has_ctm = false,
>         },
>     },
> 
> Perhaps something to try in the future.
>

Yes, agreed! Having that structure will tidy this up.
I will keep this under future work.

>>   static const u16 tidss_am65x_common_regs[DISPC_COMMON_REG_TABLE_LEN] = {
>> @@ -140,8 +142,8 @@ static const u16 tidss_am65x_common_regs[DISPC_COMMON_REG_TABLE_LEN] = {
>>     const struct dispc_features dispc_am65x_feats = {
>>       .max_pclk_khz = {
>> -        [DISPC_VP_DPI] = 165000,
>> -        [DISPC_VP_OLDI] = 165000,
>> +        [DISPC_PORT_DPI] = 165000,
>> +        [DISPC_PORT_OLDI] = 165000,
>>       },
>>         .scaling = {
>> @@ -171,7 +173,6 @@ const struct dispc_features dispc_am65x_feats = {
>>       .vp_name = { "vp1", "vp2" },
>>       .ovr_name = { "ovr1", "ovr2" },
>>       .vpclk_name =  { "vp1", "vp2" },
>> -     .vp_bus_type = { DISPC_VP_OLDI, DISPC_VP_DPI },
>>       .vp_feat = { .color = {
>>               .has_ctm = true,
>> @@ -185,6 +186,9 @@ const struct dispc_features dispc_am65x_feats = {
>>       .vid_name = { "vid", "vidl1" },
>>       .vid_lite = { false, true, },
>>       .vid_order = { 1, 0 },
>> +
>> +    .num_output_ports = 2,
>> +    .output_port_bus_type = { DISPC_PORT_OLDI, DISPC_PORT_DPI },
>>   };
>>     static const u16 tidss_j721e_common_regs[DISPC_COMMON_REG_TABLE_LEN] = {
>> @@ -229,8 +233,8 @@ static const u16 tidss_j721e_common_regs[DISPC_COMMON_REG_TABLE_LEN] = {
>>     const struct dispc_features dispc_j721e_feats = {
>>       .max_pclk_khz = {
>> -        [DISPC_VP_DPI] = 170000,
>> -        [DISPC_VP_INTERNAL] = 600000,
>> +        [DISPC_PORT_DPI] = 170000,
>> +        [DISPC_PORT_INTERNAL] = 600000,
>>       },
>>         .scaling = {
>> @@ -260,9 +264,7 @@ const struct dispc_features dispc_j721e_feats = {
>>       .vp_name = { "vp1", "vp2", "vp3", "vp4" },
>>       .ovr_name = { "ovr1", "ovr2", "ovr3", "ovr4" },
>>       .vpclk_name = { "vp1", "vp2", "vp3", "vp4" },
>> -    /* Currently hard coded VP routing (see dispc_initial_config()) */
>> -    .vp_bus_type =    { DISPC_VP_INTERNAL, DISPC_VP_DPI,
>> -              DISPC_VP_INTERNAL, DISPC_VP_DPI, },
>> +
> 
> I think this line feed is extra.

Okay! Will remove that from all SoC feat structs.

> 
>>       .vp_feat = { .color = {
>>               .has_ctm = true,
>>               .gamma_size = 1024,
>> @@ -273,6 +275,11 @@ const struct dispc_features dispc_j721e_feats = {
>>       .vid_name = { "vid1", "vidl1", "vid2", "vidl2" },
>>       .vid_lite = { 0, 1, 0, 1, },
>>       .vid_order = { 1, 3, 0, 2 },
>> +
>> +    .num_output_ports = 4,
>> +    /* Currently hard coded VP routing (see dispc_initial_config()) */
>> +    .output_port_bus_type =    { DISPC_PORT_INTERNAL, DISPC_PORT_DPI,
>> +              DISPC_PORT_INTERNAL, DISPC_PORT_DPI, },
> 
> Indent doesn't look right (but it might be just because this is a diff).

I may have missed indenting this.

> 
>>   };
>>     static const u16 *dispc_common_regmap;
>> @@ -287,12 +294,12 @@ struct dispc_device {
>>      void __iomem *base_common;
>>      void __iomem *base_vid[TIDSS_MAX_PLANES];
>> -    void __iomem *base_ovr[TIDSS_MAX_PORTS];
>> -    void __iomem *base_vp[TIDSS_MAX_PORTS];
>> +    void __iomem *base_ovr[TIDSS_MAX_VPS];
>> +    void __iomem *base_vp[TIDSS_MAX_VPS];
>>      struct regmap *oldi_io_ctrl;
>> -    struct clk *vp_clk[TIDSS_MAX_PORTS];
>> +    struct clk *vp_clk[TIDSS_MAX_VPS];
>>         const struct dispc_features *feat;
>>   @@ -300,7 +307,7 @@ struct dispc_device {
>>         bool is_enabled;
>> -    struct dss_vp_data vp_data[TIDSS_MAX_PORTS];
>> +    struct dss_vp_data vp_data[TIDSS_MAX_VPS];
>>         u32 *fourccs;
>>       u32 num_fourccs;
>> @@ -851,7 +858,7 @@ int dispc_vp_bus_check(struct dispc_device *dispc, u32 hw_videoport,
>>           return -EINVAL;
>>       }
>> -    if (dispc->feat->vp_bus_type[hw_videoport] != DISPC_VP_OLDI &&
>> +    if (dispc->feat->output_port_bus_type[hw_videoport] != DISPC_PORT_OLDI &&
> 
> Hmm, so is the hw_videoport a vp index or an output index? Sounds like
> the former, so it's not right, even if at the moment they're identical.
> We need some kind of mapping between those.
> 

It is indeed a vp index. And yes, I can come up with a mapping mechanism.

> If the mapping can be changed (or just defined in the DT), I think we
> need a variable in struct dispc_device, which tells the output to which
> a videoport is connected to. Or vice versa, I'm not sure which direction
> we need more. If the mapping is always the same on all SoC (but I don't
> think so), we can have it in the feats.
> 

As of now, the mapping is always same. But I would like to make is
generalized for future. Hence, I am considering to keep the variable in
struct dispc_device.

My question though would be, how would one be able to find which kind
of device is the port connected to, if it is connected to a bridge? For
example, in case of panels, we have a "connector_type" variable in
drm_panel which tells what kind of sink it is. But there is no such
thing in drm_bridge.

This is required because what if we can connect an videoport to either
an LVDS/OLDI bridge or a DPI bridge.

Also, implementing this might mean removal of the part of code which
confirms that the panel's "connector_type" indeed expects what the VP
can provide, unless there is a way to find out what the sink is before
calling the drm_of_find_panel_or_bridge API.


On the direction, the primary requirement of hw_videoport has been in
the tidss_dispc.c file where the HW registers are getting configured.
'hw_videoport' is a frequently passed parameter in function calls. So,
at a first glance the former option might makes more sense for
direction, i.e. to have a variable which tells the output to which a
videoport is connected to.

And while, there is also the tidss_kms.c file, which deals with
initializing encoders and attaching bridges. This is where the
output_port is required more often. But I am yet to think of a case
where the above direction could be an issue.


> Also, I wonder if output_port is a good name as it has "port" in it
> (like video port), and it's a bit long-ish. Would just "output" be
> enough? We could, of course, shorten it to OP, but that looks odd to me =).
> 

>>           fmt->is_oldi_fmt) {
>>           dev_dbg(dispc->dev, "%s: %s is not OLDI-port\n",
>>               __func__, dispc->feat->vp_name[hw_videoport]);
>> @@ -955,7 +962,7 @@ void dispc_vp_prepare(struct dispc_device *dispc, u32 hw_videoport,
>>       if (WARN_ON(!fmt))
>>           return;
>> -    if (dispc->feat->vp_bus_type[hw_videoport] == DISPC_VP_OLDI) {
>> +    if (dispc->feat->output_port_bus_type[hw_videoport] == DISPC_PORT_OLDI) {
>>           dispc_oldi_tx_power(dispc, true);
>>             dispc_enable_oldi(dispc, hw_videoport, fmt);
>> @@ -1014,7 +1021,7 @@ void dispc_vp_enable(struct dispc_device *dispc, u32 hw_videoport,
>>       align = true;
>>         /* always use DE_HIGH for OLDI */
>> -    if (dispc->feat->vp_bus_type[hw_videoport] == DISPC_VP_OLDI)
>> +    if (dispc->feat->output_port_bus_type[hw_videoport] == DISPC_PORT_OLDI)
>>           ieo = false;
>>         dispc_vp_write(dispc, hw_videoport, DISPC_VP_POL_FREQ,
>> @@ -1040,7 +1047,7 @@ void dispc_vp_disable(struct dispc_device *dispc, u32 hw_videoport)
>>     void dispc_vp_unprepare(struct dispc_device *dispc, u32 hw_videoport)
>>   {
>> -    if (dispc->feat->vp_bus_type[hw_videoport] == DISPC_VP_OLDI) {
>> +    if (dispc->feat->output_port_bus_type[hw_videoport] == DISPC_PORT_OLDI) {
>>           dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, 0);
>>             dispc_oldi_tx_power(dispc, false);
>> @@ -1116,10 +1123,10 @@ enum drm_mode_status dispc_vp_mode_valid(struct dispc_device *dispc,
>>                        const struct drm_display_mode *mode)
>>   {
>>      u32 hsw, hfp, hbp, vsw, vfp, vbp;
>> -    enum dispc_vp_bus_type bus_type;
>> +    enum dispc_port_bus_type bus_type;
>>      int max_pclk;
>> -    bus_type = dispc->feat->vp_bus_type[hw_videoport];
>> +    bus_type = dispc->feat->output_port_bus_type[hw_videoport];
>>      max_pclk = dispc->feat->max_pclk_khz[bus_type];
>> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.h b/drivers/gpu/drm/tidss/tidss_dispc.h
>> index e49432f0abf5..30fb44158347 100644
>> --- a/drivers/gpu/drm/tidss/tidss_dispc.h
>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.h
>> @@ -50,11 +50,11 @@ struct dispc_errata {
>>       bool i2000; /* DSS Does Not Support YUV Pixel Data Formats */
>>   };
>> -enum dispc_vp_bus_type {
>> -    DISPC_VP_DPI,        /* DPI output */
>> -    DISPC_VP_OLDI,        /* OLDI (LVDS) output */
>> -    DISPC_VP_INTERNAL,    /* SoC internal routing */
>> -    DISPC_VP_MAX_BUS_TYPE,
>> +enum dispc_port_bus_type {
>> +    DISPC_PORT_DPI,            /* DPI output */
>> +    DISPC_PORT_OLDI,        /* OLDI (LVDS) output */
>> +    DISPC_PORT_INTERNAL,        /* SoC internal routing */
>> +    DISPC_PORT_MAX_BUS_TYPE,
> 
> Okay, so here you have just "port", not "output_port". In the DT,
> they're ports, so... Maybe we could use that name too, and for video
> port always use "vp". The current "hw_videoport" could be easily
> mistaken with "port".

I see what you are saying and how somebody could confusre hw_videoport
for a physical connection (i.e. port). I have always understoof
hw_videoport to be a thing of the actual VP inside the SoC, but that may
be because I have been working on this, and not just trying to
understand the code from a high level.

How about if I change the output_port to "out_port"? I am okay to keep
"output" as the name to. I am saying this becuase I think, only keeping
"port" might just confuse more, as you mentioned above.

And then we can change "hw_videoport" to "vp_index", perhaps, or even
keep that as it is? Becuase if we do have a VP structure in future
like you suggested above, "vps" and "vp" would become a close overlap.
For eg, "vps[vp]".

How do these sound to you?

> 
> I don't recall why I chose to use "hw" prefix there. I think I wanted to
> separate it from some other videoport, but... I don't know what that
> "other" is =).
> 

Perhaps because just a "videoport" might be confused with a connector on
the board, as in "HDMI port"? And the prefix might be a way to clarify
that its the DSS controller's VP. =)


Regards
Aradhya