[Nouveau] Questions about some PFB registers on NVAC cards

[Pierre Moreau]

Hi Robert,

After trying to write a proper patch for Nouveau, we realised we were missing a few pieces of information.

----- Mail original -----
> Hi Robert,
>
> Thanks a lot for your response!
>
> ----- Mail original -----
> > On Wed, Oct 22, 2014 at 12:55:23AM +0200, pierre.morrow at free.fr
> > wrote:
> > [...]
> > > After some investigation, I found that enabling bit 1 of register
> > > 100c14 fixes
> > > the issue on that card. Other NVAC cards are working great
> > > without
> > > that trick,
> > > and it seems they have that bit enabled by default. What is the
> > > role of that
> > > bit, and when should it be turned on?
> >
> > Register 100c14 controls a feature of the integrated GPU's memory
> > interface
> > called the "poller".  The pollers exist on MCP77/78 and MCP79/7A to
> > ensure
> > that certain types of writes have flushed all the way to system
> > memory.  (I
> > think this is needed to ensure proper ordering of memory
> > transactions.)
> >
> > There are actually three important bits in that register, which
> > control three
> > pollers:
> >
> > NV_PFB_NISO_POLLER_CFG
> >                                                0x00100c14
> > NV_PFB_NISO_POLLER_CFG_DNISO_ENABLE
> >                                          0:0
> > NV_PFB_NISO_POLLER_CFG_DNISO_ENABLE_DISABLED
> >                          0x00000000
> > NV_PFB_NISO_POLLER_CFG_DNISO_ENABLE_ENABLED
> >                           0x00000001
> > NV_PFB_NISO_POLLER_CFG_HOSTNB_ENABLE
> >                                         1:1
> > NV_PFB_NISO_POLLER_CFG_HOSTNB_ENABLE_DISABLED
> >                         0x00000000
> > NV_PFB_NISO_POLLER_CFG_HOSTNB_ENABLE_ENABLED
> >                          0x00000001
> > NV_PFB_NISO_POLLER_CFG_FLUSH_ENABLE
> >                                        16:16
> > NV_PFB_NISO_POLLER_CFG_FLUSH_ENABLE_DISABLED
> >                          0x00000000
> > NV_PFB_NISO_POLLER_CFG_FLUSH_ENABLE_ENABLED
> >                           0x00000001

Out of curiosity, what do DNISO and HOSTNB mean?

> >
> > > Before enabling 100c14's bit 1, the Nvidia driver writes some
> > > value
> > > into 100c1c.
> > > Leaving the default value, or writing some random value seemed to
> > > have no
> > > effect. What is this register used for?
> >
> > 100c1c is one of three registers which control the (upper bits of
> > the
> > 32-byte
> > aligned) memory locations that the pollers use:

So, as the memory location is 32-byte aligned the last 8 bits of the address are uncessary. 100c1c and the others hold 32 bits. So are the missing 24 bits of the address forced to zero or do we need to specify them somewhere?

Here is the patch so far, where priv->r100c08 is an address to an empty dma page:

    diff --git a/nvkm/subdev/fb/nv50.c b/nvkm/subdev/fb/nv50.c
    index 4150b0d..1a0a94e 100644
    --- a/nvkm/subdev/fb/nv50.c
    +++ b/nvkm/subdev/fb/nv50.c
    @@ -295,6 +296,19 @@ nv50_fb_init(struct nouveau_object *object)
             */
            nv_wr32(priv, 0x100c08, priv->r100c08 >> 8);
    
    +       /* Enable NISO poller for various clients and set their associated
    +        * read address, only for MCP77/78 and MCP79/7A. (fd#25701)
    +        */
    +       if ((nv_device(priv)->chipset == 0xaa || nv_device(priv)->chipset == 0xac)
    +                       && !nv_rd32(priv, 0x100c14)) {
    +               nv_wr32(priv, 0x100c18, priv->r100c08 >> 8);
    +               nv_mask(priv, 0x100c14, 0x00000000, 0x00000001);
    +               nv_wr32(priv, 0x100c1c, priv->r100c08 >> 8);
    +               nv_mask(priv, 0x100c14, 0x00000000, 0x00000002);
    +               nv_wr32(priv, 0x100c24, priv->r100c08 >> 8);
    +               nv_mask(priv, 0x100c14, 0x00000000, 0x00010000);
    +       }
    +
            /* This is needed to get meaningful information from 100c90
             * on traps. No idea what these values mean exactly. */
            nv_wr32(priv, 0x100c90, impl->trap);

Thanks,

Pierre


> >
> > #define NV_PFB_NISO_POLLER_DNISO_BASE_ADR
> >                     0x00100C18
> > #define NV_PFB_NISO_POLLER_HOSTNB_BASE_ADR
> >                    0x00100C1C
> > #define NV_PFB_NISO_FLUSH_CARVEOUT_ADR
> >                        0x00100C24
> >
> > Each of these should point to at least 32 bytes of otherwise-unused
> > FB
> > memory, if the poller is enabled.
> >
> > The proprietary driver enables all three pollers for GPUs that have
> > them, when
> > memory is not local (i.e., when using a sysmem carveout rather than
> > dedicated
> > video memory).
> >
> > I'm not sure why this seems to only be necessary on some systems
> > and
> > not
> > others.
>
> I didn't meant that it wasn't necessary on other systems, just that
> it was enabled by default on those systems so they would work even
> if Nouveau didn't set the pollers.
>
> >
> > - Robert
> >
>
> Regards,
>
> Pierre
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