[Nouveau] DCB 4.1 spec update
Ben Skeggs
skeggsb at gmail.com
Sun Dec 14 13:40:32 PST 2014
On Sat, Dec 13, 2014 at 6:42 PM, Andy Ritger <aritger at nvidia.com> wrote:
> On Wed, Dec 10, 2014 at 07:46:16AM +1000, Ben Skeggs wrote:
>> On Wed, Dec 10, 2014 at 7:36 AM, Ben Skeggs <skeggsb at gmail.com> wrote:
>> > On Wed, Dec 10, 2014 at 4:26 AM, Andy Ritger <aritger at nvidia.com> wrote:
>> >> Hi,
>> > Hey Andy,
>> >
>> >>
>> >> The VBIOS on GM20x GPUs uses a slightly updated version of the DCB.
>> >> I've posted an updated DCB spec here:
>> >>
>> >> ftp://download.nvidia.com/open-gpu-doc/DCB/2/DCB-4.x-Specification.html
>> >>
>> >> You can diff it against the previous version:
>> >>
>> >> ftp://download.nvidia.com/open-gpu-doc/DCB/1/DCB-4.0-Specification.html
>> >>
>> >> to see what changed (sorry for having to diff html files). The biggest
>> >> differences are Serial Output Resource (SOR) assignment, and the updated
>> >> Communications Control Block layout.
>> > Thanks for the heads-up on the update. The SOR assignment changes
>> > explain some things I noticed when bringing up the GM204 you guys sent
>> > me :)
>> One question I have on making proper use of this is how should the RM
>> determine which DCB entry (and hence, the correct pad macro) to use
>> based on the SorSetControl index from the supervisor?
>
> Hi Ben.
>
> Yes, this is a little confusing. I had to review for myself and consult
> with one of our VBIOS experts.
>
> Below is my understanding. You probably know most of this already,
> so sorry for stating anything obvious.
>
> Terminology:
>
> SOR: Serial Output Resource. What is used to drive LVDS, TMDS, and
> DisplayPort. GM20x has four SORs.
>
> SOR Sublink: An individual link within an SOR. Each SOR has two links
> (SOR LinkA and SOR LinkB, per SOR).
>
> Macro: Receives signal from one or two SOR sublinks, and transmits to
> a connector. GM20x has four Macros.
>
> Macro Link (aka Pad Link): An individual link within a Macro. The first
> three Macros have two Macro Links each, and the fourth has one
> Macro Link. The Macro Links are labeled A - G.
>
> In GM20x, we added an "SOR Crossbar" between the SORs and the Macros,
> such that any SOR Sublink can drive any Macro Link.
>
> The registers to control the SOR Crossbar are 0x00612308+(i)*128:
>
> #define NV_PDISP_CLK_REM_LINK_CTRL(i) (0x00612308+(i)*128) /* RW-4A */
> #define NV_PDISP_CLK_REM_LINK_CTRL__SIZE_1 7 /* */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND 3:0 /* RWIVF */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_INIT 0x00000000 /* RWI-V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_NONE 0x00000000 /* RW--V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR0 0x00000001 /* RW--V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR1 0x00000002 /* RW--V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR2 0x00000003 /* RW--V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR3 0x00000004 /* RW--V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR 4:4 /* RWIVF */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR_INIT 0x00000000 /* RWI-V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR_PRIMARY 0x00000000 /* RW--V */
> #define NV_PDISP_CLK_REM_LINK_CTRL_FRONTEND_SOR_SECONDARY 0x00000001 /* RW--V */
>
> The index (i) is the Macro Link number (0 through 6). You can direct
> the Macro Link to listen to one of the four SORs, and either LinkA
> (SOR_PRIMARY) or LinkB (SOR_SECONDARY) of the selected SOR.
>
> Note the default Macro Link to SOR Sublink assignment is NONE, so you'll need
> to program NV_PDISP_CLK_REM_LINK_CTRL to drive any SORs not set up by
> the VBIOS.
>
> Looking at the DCB spec, bits 24-27 in the Display Path Information
> entry will indicate which Macro the entry is talking about:
>
> For Internal and External DFPs we can use any of the available SORs
> but the Pad Macro is fixed per Device Entry.
> Bit 0 = Pad Macro 0 (Pad Links A and B)
> Bit 1 = Pad Macro 1 (Pad Links C and D)
> Bit 2 = Pad Macro 2 (Pad Links E and F)
> Bit 3 = Pad Macro 3 (Pad Link G)
>
> (AIUI, only one bit will be set per entry)
>
> And then bits 4-5 in the the DFP Specific Information table indicate
> which Macro Link(s) (aka Pad Link(s)) within the Macro the entry is
> talking about:
>
> For DCB 4.1: For TMDS/LVDS/DP this field describes which links of
> the Pad Macro are routed to the connector on the board.
> Bit 0: Pad Link 0
> Bit 1: Pad Link 1
>
> The SorSetControl index, as used in the supervisor interrupt, indicates
> one of the four SORs, and you can refer to the SOR Crossbar configuration
> to determine which Macro Link(s) are listening to the SOR Links of
> that SOR. From the Macro Links, you should be able to correlate to
> DCB entries.
>
> For an example topology, our reference GTX 980 board has the following layout:
>
> * Pad links A+B and DAC1 are connected to the DVI-I connector
> * Link C (Macro 1 Pad Link 0) is connected to the HDMI-A connector
> * Link D (Macro 1 Pad Link 1) is connected to a DP connector
> * Link E (Macro 2 Pad Link 0) is connected to a DP connector
> * Link F (Macro 2 Pad Link 1) is connected to a DP connector
>
> Except for DP multi-stream, one SOR should be used to drive a connector.
Hm, is this true? I've not looked at MST on GM204 yet, but earlier
Keplers it was still one SOR but multiple heads attached to it.
>
> The setup sequence would normally be:
> * Decide which connectors you want to drive.
> * Check which link (links for duallink-DVI) to use with that connector, per the DCB.
It's this step I was unsure of. The only information channel we
currently have between the "user" side of display and the supervisor
is what can be pushed through core channel methods. I guess a more
explicit way to phrase what I was wanting to know is: Are there any
additional methods for the user of core to configure the sor->macro
routing, or is this something that is up to the driver to implement
however it sees fit?
Thanks again!
Ben.
> * Assign an unused SOR to those link(s) via the NV_PDISP_CLK_REM_LINK_CTRL registers.
> * Use SorSetControl to attach a head to that SOR.
>
> I hope that makes sense.
>
> Thanks,
> - Andy
>
>
>> Thanks,
>> Ben.
>>
>> >
>> > Ben.
>> >
>> >>
>> >> I hope that is helpful,
>> >> - Andy
>> >>
>> >> _______________________________________________
>> >> Nouveau mailing list
>> >> Nouveau at lists.freedesktop.org
>> >> http://lists.freedesktop.org/mailman/listinfo/nouveau
More information about the Nouveau
mailing list