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SubjectRE: [PATCH] usb: dwc3: Enable the USB snooping
Date
Hi Felipe,

On Monday, June 17, 2019 20:53, Felipe Balbi wrote:
> Hi,
>
> Ran Wang <ran.wang_1@nxp.com> writes:
> > Hi Felipe,
> >
> > On Thursday, May 30, 2019 17:09, Ran Wang wrote:
> >>
> >> <snip>
> >> > >> >> > /* Global Debug Queue/FIFO Space Available Register */
> >> > >> >> > #define DWC3_GDBGFIFOSPACE_NUM(n) ((n) & 0x1f)
> >> > >> >> > #define DWC3_GDBGFIFOSPACE_TYPE(n) (((n) << 5) & 0x1e0)
> >> > >> >> > @@ -859,6 +867,7 @@ struct dwc3_scratchpad_array {
> >> > >> >> > * 3 - Reserved
> >> > >> >> > * @imod_interval: set the interrupt moderation interval in 250ns
> >> > >> >> > * increments or 0 to disable.
> >> > >> >> > + * @dma_coherent: set if enable dma-coherent.
> >> > >> >>
> >> > >> >> you're not enabling dma coherency, you're enabling cache snooping.
> >> > >> >> And this property should describe that. Also, keep in mind
> >> > >> >> that different devices may want different cache types for
> >> > >> >> each of those fields, so your property would have to be a lot
> >> > >> >> more complex. Something
> >> > like:
> >> > >> >>
> >> > >> >> snps,cache-type = <foobar "cacheable">, <baz "cacheable">, ...
> >> > >> >>
> >> > >> >> Then driver would have to parse this properly to setup GSBUSCFG0.
> >> > >
> >> > > According to the DesignWare Cores SuperSpeed USB 3.0 Controller
> >> > > Databook (v2.60a), it has described Type Bit Assignments for all
> >> > > supported
> >> > master bus type:
> >> > > AHB, AXI3, AXI4 and Native. I found the bit definition are
> >> > > different among
> >> > them.
> >> > > So, for the example you gave above, feel a little bit confused.
> >> > > Did you mean:
> >> > > snps,cache-type = <DATA_RD "write allocate">, <DESC_RD
> >> > > "cacheable">, <DATA_WR "bufferable">, <DESC_WR "read allocate">
> >> >
> >> > yeah, something like that.
> >>
> >> I think DATA_RD should be a macro, right? So, where I can put its define?
> >> Create a dwc3.h in include/dt-bindings/usb/ ?
> >
> > Could you please give me some advice here? I'd like to prepare next
> > version patch after getting this settled.
> >
> >> Another question about this remain open is: DWC3 data book's Table
> >> 6-5 Cache Type Bit Assignments show that bits definition will differ
> >> per MBUS_TYPEs as
> >> below:
> >> ----------------------------------------------------------------
> >> MBUS_TYPE| bit[3] |bit[2] |bit[1] |bit[0]
> >> ----------------------------------------------------------------
> >> AHB |Cacheable |Bufferable |Privilegge |Data
> >> AXI3 |Write Allocate|Read Allocate|Cacheable |Bufferable
> >> AXI4 |Allocate Other|Allocate |Modifiable |Bufferable
> >> AXI4 |Other Allocate|Allocate |Modifiable |Bufferable
> >> Native |Same as AXI |Same as AXI |Same as AXI|Same as AXI
> >> ----------------------------------------------------------------
> >> Note: The AHB, AXI3, AXI4, and PCIe busses use different names for
> >> certain signals, which have the same meaning:
> >> Bufferable = Posted
> >> Cacheable = Modifiable = Snoop (negation of No Snoop)
> >>
> >> For Layerscape SoCs, MBUS_TYPE is AXI3. So I am not sure how to use
> >> snps,cache-type = <DATA_RD "write allocate">, to cover all MBUS_TYPE?
> >> (you can notice that AHB and AXI3's cacheable are on different bit)
> >> Or I just need to handle AXI3 case?
> >
> > Also on this open. Thank you in advance.
>
> You could pass two strings and let the driver process them. Something
> like:
>
> snps,cache_type = <"data_wr" "write allocate">, <"desc_rd"
> "cacheable">...
>
> And so on. The only thing missing is for the mbus_type to be known by the driver.
> Is that something we can figure out on any of the HWPARAMS registers or does
> it have to be told explicitly?

I have checked Layerscape Reference manual, HWPARAMS0~8 doesn't contain mbus_type
Info, and I didn't know where have declared it explicitly.

> Another option would be to pass a string followed by one hex digit for the bits:
>
> snps,cache_type = <"data_wr" 0x8>, <"desc_rd" 0x2>...;
>
> Then we don't need to describe mbus_type since the bits are what matters.

Yes, it's also what we prefer to use, it will be more flexible, I can add above Table
6-5 Cache Type Bit Assignments in binding to help user decide which value they
would use.

I would submit another version of patch for further review, thank you very much.

Regards,
Ran

> Rob, any comments?
>
> --
> balbi

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