Re: [RFC 3/3] CMDQ: Mediatek CMDQ driver

[Horng-Shyang Liao <hs.liao@mediatek.com>]

On Mon, 2016-02-01 at 18:22 +0800, Daniel Kurtz wrote:
> On Mon, Feb 1, 2016 at 2:20 PM, Horng-Shyang Liao <hs.liao@mediatek.com> wrote:
> > On Mon, 2016-02-01 at 12:15 +0800, Daniel Kurtz wrote:
> >> On Mon, Feb 1, 2016 at 10:04 AM, Horng-Shyang Liao <hs.liao@mediatek.com> wrote:
> >> >
> >> > On Fri, 2016-01-29 at 21:15 +0800, Daniel Kurtz wrote:
> >> > > On Fri, Jan 29, 2016 at 8:24 PM, Horng-Shyang Liao <hs.liao@mediatek.com> wrote:
> >> > > > On Fri, 2016-01-29 at 16:42 +0800, Daniel Kurtz wrote:
> >> > > >> On Fri, Jan 29, 2016 at 3:39 PM, Horng-Shyang Liao <hs.liao@mediatek.com> wrote:
> >> > > >> > Hi Dan,
> >> > > >> >
> >> > > >> > Many thanks for your comments and time.
> >> > > >> > I reply my plan inline.
> >> > > >> >
> >> > > >> >
> >> > > >> > On Thu, 2016-01-28 at 12:49 +0800, Daniel Kurtz wrote:
> >> > > >> >> Hi HS,
> >> > > >> >>
> >> > > >> >> Sorry for the delay.  It is hard to find time to review a >3700 line
> >> > > >> >> driver :-o in detail....
> >> > > >> >>
> >> > > >> >> Some review comments inline, although I still do not completely
> >> > > >> >> understand how all that this driver does and how it works.
> >> > > >> >> I'll try to find time to go through this driver in detail again next
> >> > > >> >> time you post it for review.
> >> > > >> >>
> >> > > >> >> On Tue, Jan 19, 2016 at 9:14 PM,  <hs.liao@mediatek.com> wrote:
> >> > > >> >> > From: HS Liao <hs.liao@mediatek.com>
> >> > > >> >> >
> >> > > >> >> > This patch is first version of Mediatek Command Queue(CMDQ) driver. The
> >> > > >> >> > CMDQ is used to help read/write registers with critical time limitation,
> >> > > >> >> > such as updating display configuration during the vblank. It controls
> >> > > >> >> > Global Command Engine (GCE) hardware to achieve this requirement.
> >> > > >> >> > Currently, CMDQ only supports display related hardwares, but we expect
> >> > > >> >> > it can be extended to other hardwares for future requirements.
> >> > > >> >> >
> >> > > >> >> > Signed-off-by: HS Liao <hs.liao@mediatek.com>
> >> > > >> >>
> >> > > >> >> [snip]
> >> > > >> >>
> >> > > >> >> > diff --git a/drivers/soc/mediatek/mtk-cmdq.c b/drivers/soc/mediatek/mtk-cmdq.c
> >> > > >> >> > new file mode 100644
> >> > > >> >> > index 0000000..7570f00
> >> > > >> >> > --- /dev/null
> >> > > >> >> > +++ b/drivers/soc/mediatek/mtk-cmdq.c
> >> > > >
> >> > > > [snip]
> >> > > >
> >> > > >> >> > +static const struct cmdq_subsys g_subsys[] = {
> >> > > >> >> > +       {0x1400, 1, "MMSYS"},
> >> > > >> >> > +       {0x1401, 2, "DISP"},
> >> > > >> >> > +       {0x1402, 3, "DISP"},
> >> > > >> >>
> >> > > >> >> This isn't going to scale.  These addresses could be different on
> >> > > >> >> different chips.
> >> > > >> >> Instead of a static table like this, we probably need specify to the
> >> > > >> >> connection between gce and other devices via devicetree phandles, and
> >> > > >> >> then use the phandles to lookup the corresponding device address
> >> > > >> >> range.
> >> > > >> >
> >> > > >> > I will define them in device tree.
> >> > > >> > E.g.
> >> > > >> > cmdq {
> >> > > >> >   reg_domain = 0x14000000, 0x14010000, 0x14020000
> >> > > >> > }
> >> > > >>
> >> > > >> The devicetree should only model hardware relationships, not software
> >> > > >> considerations.
> >> > > >>
> >> > > >> Is the hardware constraint here for using gce with various other
> >> > > >> hardware blocks?  I think we already model this by only providing a
> >> > > >> gce phandle in the device tree nodes for those devices that can use
> >> > > >> gce.
> >> > > >>
> >> > > >> Looking at the driver closer, as far as I can tell, the whole subsys
> >> > > >> concept is a purely software abstraction, and only used to debug the
> >> > > >> CMDQ_CODE_WRITE command.  In fact, AFAICT, everything would work fine
> >> > > >> if we just completely removed the 'subsys' concept, and just passed
> >> > > >> through the raw address provided by the driver.
> >> > > >>
> >> > > >> So, I recommend just removing 'subsys' completely from the driver -
> >> > > >> from this array, and in the masks.
> >> > > >>
> >> > > >> Instead, if there is an error on the write command, just print the
> >> > > >> address that fails.  There are other ways to deduce the subsystem from
> >> > > >> a physical address.
> >> > > >>
> >> > > >> Thanks,
> >> > > >>
> >> > > >> -Dan
> >> > > >
> >> > > > Hi Dan,
> >> > > >
> >> > > > Subsys is not just for debug.
> >> > > > Its main purpose is to transfer CPU address to GCE address.
> >> > > > Let me explain it by "write" op,
> >> > > > I list a code segment from cmdq_rec_append_command().
> >> > > >
> >> > > >         case CMDQ_CODE_WRITE:
> >> > > >                 subsys = cmdq_subsys_from_phys_addr(cqctx, arg_a);
> >> > > >                 if (subsys < 0) {
> >> > > >                         dev_err(dev,
> >> > > >                                 "unsupported memory base address 0x%08x\n",
> >> > > >                                 arg_a);
> >> > > >                         return -EFAULT;
> >> > > >                 }
> >> > > >
> >> > > >                 *cmd_ptr++ = arg_b;
> >> > > >                 *cmd_ptr++ = (CMDQ_CODE_WRITE << CMDQ_OP_CODE_SHIFT) |
> >> > > >                              (arg_a & CMDQ_ARG_A_WRITE_MASK) |
> >> > > >                              ((subsys & CMDQ_SUBSYS_MASK) << CMDQ_SUBSYS_SHIFT);
> >> > > >                 break;
> >> > > >
> >> > > > Subsys is mapped from physical address via cmdq_subsys_from_phys_addr(),
> >> > > > and then it becomes part of GCE command via ((subsys & CMDQ_SUBSYS_MASK)
> >> > > > << CMDQ_SUBSYS_SHIFT) .
> >> > > > Only low bits of physical address are the same as GCE address.
> >> > > > We can get it by (arg_a & CMDQ_ARG_A_WRITE_MASK).
> >> > > > MASK is used to define how many bits are valid for this op.
> >> > > > So, GCE address = subsys + valid low bits.
> >> > >
> >> > > How are these upper bits of the "GCE address" defined?
> >> > > In other words, for a given SoC, how is the mapping between physical
> >> > > io addresses to GCE addresses defined?
> >> > > Is this mapping fixed by hardware?
> >>
> >> Please answer the detailed technical questions:
> >>
> >> How are these upper bits of the "GCE address" defined?
> >
> > A GCE command is arg_a + arg_b. Both of them have 32 bits length.
> > arg_a is op + subsys + addr, and arg_b is value.
> > subsys + addr is less than 32bits, so we need to map address range to
> > subsys.
> > The mapping rule is defined by hardware.
> >
> >> In other words, for a given SoC, how is the mapping between physical
> >> io addresses to GCE addresses defined?
> >
> > It is (b).
> >
> >>
> >> (a) Does the GCE remap a continuous device IO address range?
> >>
> >> AFAICT, the  defines an MT8173 specific mapping of:
> >>
> >> For example, the g_subsys table above seems to imply that the MT8173
> >> gce maps all of:
> >>   0x1400ffff:0x141fffff => 0x010000:0x1fffff
> >>
> >> (b) Or, are the upper 5 bits of the "gce address" significant, and via
> >> hardware it can map a disjoint groups of device addresses into the
> >> continuous GCE address space, and really there are 0x1f distinct 64k
> >> mappings:
> >>
> >> mmsys (1) : 0x14000000:0x1400ffff => 0x010000:0x01ffff
> >> disp  (2) : 0x14010000:0x1401ffff => 0x020000:0x02ffff
> >> disp  (3) : 0x14020000:0x1402ffff => 0x030000:0x03ffff
> >> ...
> >> ???? (1f) : 0x141fffff:0x141fffff => 0x1f0000:0x1fffff
> >>
> >> If the mapping is fixed and continuous (a), then I think all we need
> >> is a single dts entry for the gce node that describes how it performs
> >> this mapping.  And then, the gce consumers can just pass in their
> >> regular physical addresses, and the gce driver can remap them directly
> >> to gce addresses.
> >>
> >> WDYT?
> >
> > How about this?
> > hardware_module = <address_base subsys_id mask>;
> > So, the result is
> > mmsys_config_base = <0x14000000 1 0xffff0000>;
> > disp_rdma_config_base = <0x14010000 2 0xffff0000>;
> > disp_mutex_config_base = <0x14020000 3 0xffff0000>;
> 
> What uses ID 0 and 4 - 0x1f?

Subsys is defined by GCE hardware, and other IDs are reserved currently.

> According to mt8173.dtsi, here are the blocks in the address ranges above:
> 
> @1400:
>   mmsys: clock-controller@14000000
>   ovl0: ovl@1400c000
>   ovl1: ovl@1400d000
>   rdma0: rdma@1400e000
>   rdma1: rdma@1400f000
> 
> @1401:
>   rdma2: rdma@14010000
>   wdma0: wdma@14011000
>   wdma1: wdma@14012000
>   color0: color@14013000
>   color1: color@14014000
>   aal@14015000
>   gamma@14016000
>   merge@14017000
>   split0: split@14018000
>   split1: split@14019000
>   ufoe@1401a000
>   dsi0: dsi@1401b000
>   dsi1: dsi@1401c000
>   dpi0: dpi@1401d000
>   pwm0: pwm@1401e000
>   pwm1: pwm@1401f000
> 
> @1402:
>   mutex: mutex@14020000
>   od@14023000
>   larb0: larb@14021000
>   smi_common: smi@14022000
>   hdmi0: hdmi@14025000
>   larb4: larb@14027000
> 
> I assume that the gce will work with any of the devices in those
> ranges, not just "mmsys", "rdma" and "mutex", right?   (Also, notice

That's right.

> there are two "rdma" in the @1400 range, so rdma is really not a good
> name for @1401)

I think we can just use index.
disp0_config_base = <0x14000000 1 0xffff0000>;
disp1_config_base = <0x14010000 2 0xffff0000>;
disp2_config_base = <0x14020000 3 0xffff0000>;

> Further, it looks like the gce just maps a large device address range
> starting at 0x14000000 to (21-bit) gce address 0x010000, rather than
> 31 individually addressable 64k "subsys" blocks.  Is there a counter
> example that I am missing?

>From GCE's point of view,
it's 32 (0x0~0x1f) individually addressable 64k "subsys" blocks.
Currently, we don't have a counter example since all display related
address are put together.

> -Dan

Thanks,
HS Liao

> >
> >> -Dan
> >>
> >> >
> >> > Yes, this mapping is fixed by hardware.
> >> >
> >> > > Does it vary for different SoCs?
> >> >
> >> > Yes, it varies for different SoCs.
> >> >
> >> > >
> >> > > -Dan
> >> > >
> >> > > > That's why we need to know the mapping between the range of physical
> >> > > > address and subsys.
> >> > > > Please guide us a better way to code such requirement.
> >> > > > Thanks for your help.
> >> > > >
> >> > > > Thanks,
> >> > > > HS Liao
> >> > > >
> >> >
> >> > Thanks,
> >> > HS Liao
> >> >
> >
> > Thanks,
> > HS Liao
> >