RE: [PATCH] usb: dwc3: Enable the USB snooping

[Ran Wang]

Hi Felipe,

On Monday, June 24, 2019 13:58, Felipe Balbi wrote:
> 
> Hi,
> 
> Ran Wang <ran.wang_1@xxxxxxx> writes:
> >> >> > >> >> >  /* 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.

For this option, looks like DTC doesn't allow form of <"data_wr" 0x8>, <"desc_rd" 0x2>... 
It will report error when compiling:

DTC     arch/arm64/boot/dts/freescale/fsl-ls1088a-rdb.dtb
Error: arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi:383.23-24 syntax error
FATAL ERROR: Unable to parse input tree
scripts/Makefile.lib:294: recipe for target 'arch/arm64/boot/dts/freescale/fsl-ls1088a-qds.dtb' failed
make[2]: *** [arch/arm64/boot/dts/freescale/fsl-ls1088a-qds.dtb] Error 1
make[2]: *** Waiting for unfinished jobs....
Error: arch/arm64/boot/dts/freescale/fsl-ls1088a.dtsi:383.23-24 syntax error
FATAL ERROR: Unable to parse input tree

One of the solution I can figure out is to use macro to replace "data_wr", like below:
<DATA_WR 0x8>, <DESC_RD 0x2>...

However, it will require creating file in include/dt-bindings/usb/dwc3.h to
place macro definitions.

Or may I use:  "data_wr", <0x8>,  "desc_rd",  <0x2>... ?

Thanks & Regards,
Ran

> > 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.
> 
> cool, thanks
> 
> --
> balbi