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

[Horng-Shyang Liao]

On Wed, 2016-02-03 at 09:40 +0800, Cawa Cheng (éæç) wrote:
> 
> -----Original Message-----
> From: djkurtz@xxxxxxxxxx [mailto:djkurtz@xxxxxxxxxx] On Behalf Of Daniel Kurtz
> Sent: Wednesday, February 03, 2016 12:22 AM
> To: Hs Liao (ååç)
> Cc: Rob Herring; Matthias Brugger; Sascha Hauer; open list:OPEN FIRMWARE AND...; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; moderated list:ARM/Mediatek SoC support; srv_heupstream; Sascha Hauer; Philipp Zabel; Nicolas Boichat; CK Hu (èäå); Cawa Cheng (éæç); Bibby Hsieh (èæé); YT Shen (æåé); Daoyuan Huang (ééå); Damon Chu (æåè); Josh-YC Liu (åèè); Glory Hung (ææç); Yong Wu (åå)
> Subject: Re: [RFC 3/3] CMDQ: Mediatek CMDQ driver
> 
> On Tue, Feb 2, 2016 at 2:48 PM, Horng-Shyang Liao <hs.liao@xxxxxxxxxxxx> wrote:
> > 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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> wrote:
> >> >> > > >> >> > From: HS Liao <hs.liao@xxxxxxxxxxxx>
> >> >> > > >> >> >
> >> >> > > >> >> > 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@xxxxxxxxxxxx>
> >> >> > > >> >>
> >> >> > > >> >> [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.
> 
> Ok, in this case, perhaps we should treat the GCE like an IOMMU, and have its binding define 32 slots or channels.
> Then, any device that wishes to send the GCE commands for its address range should register a phandle to the gce, including the corresponding slot.
> 
> For example:
> 
> include/.../gce.h
> include/dt-bindings/../mediatek-gce.h
> #define GCE_SLOT_1  1
> ...
> 
> arch/arm64/boot/dts/mediatek/mt8173.dtsi:
> 
> &ovl0: {
>   mediatek,gce = <&gce GCE_SLOT_1>;
> };
> 
> &ovl1: {
>   mediatek,gce = <&gce GCE_SLOT_1>;
> };
> 
> &rdma2: {
>   mediatek,gce = <&gce GCE_SLOT_2>;
> };
> 
> &mutex: {
>   mediatek,gce = <&gce GCE_SLOT_3>;
> };
> 
> &od: {
>   mediatek,gce = <&gce GCE_SLOT_3>;
> };
> 
> Then, as each platform driver is probed, it can use the phandle to look up its corresponding gce slot instance, retrieving an (opaque) pointer to a struct gce_slot.
> The gce driver can have a set of constant tables matching the slots to address ranges for particular per-soc compatibles, one of which is loaded on probe.
> Later, when the device (gce consumer) wants to send a gce write command, it passes in the gce_slot as an argument, and the gce driver can do the corresponding lookup of subsys value and mask out the provided *device virtual* address.  In this way, you also no longer need to convert the devices iomap'ed addresses into physical addresses before passing them to the gce.
> 
> WDYT?
> 
> -Dan

Hi Dan,

Thanks for your comment.
This solution looks good to me.
I will change it as your suggestion.

But, I have a question about 'mask out the provided *device virtual*
address'.
Are lower 16-bits (or 24-bits for JUMP op) of device virtual address the
same as device physical address?
If not, we still need to pass in physical address into CMDQ driver.

Thanks,
HS Liao