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

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Message-ID: <AM5PR0402MB2865F3735D808E1BC9F67968F1180@AM5PR0402MB2865.eurprd04.prod.outlook.com>
Date:   Thu, 30 May 2019 09:08:36 +0000
From:   Ran Wang <ran.wang_1@....com>
To:     Felipe Balbi <balbi@...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@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH] usb: dwc3: Enable the USB snooping

Hi Felipe,

On Tuesday, May 28, 2019 18:20, Felipe Balbi 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/ ?

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?

Regards,
Ran