linux-kernel - RE: [PATCH] usb: dwc3: Enable the USB snooping

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Date:   Mon, 24 Jun 2019 08:58:16 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Ran Wang <ran.wang_1@....com>, Rob Herring <robh+dt@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list\:DESIGNWARE USB3 DRD IP DRIVER" 
        <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
        Leo Li <leoyang.li@....com>
Subject: RE: [PATCH] usb: dwc3: Enable the USB snooping


Hi,

Ran Wang <ran.wang_1@....com> 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.
>
> 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