RE: [PATCH v3 2/3] USB3/DWC3: Add property "snps, incr-burst-type-adjustment" for INCR burst type

[Felipe Balbi <balbi@kernel.org>]

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Hi,

Jerry Huang <jerry.huang@nxp.com> writes:
>> > On Thu, Dec 22, 2016 at 8:52 PM, Jerry Huang <jerry.huang@nxp.com>
>> wrote:
>> > > Hi, Rob,
>> > >> -----Original Message-----
>> > >> From: Rob Herring [mailto:robh@kernel.org]
>> > >> Sent: Friday, December 23, 2016 2:45 AM
>> > >> To: Jerry Huang <jerry.huang@nxp.com>
>> > >> Cc: balbi@kernel.org; mark.rutland@arm.com;
>> > >> catalin.marinas@arm.com; will.deacon@arm.com;
>> > >> linux@armlinux.org.uk; devicetree@vger.kernel.org;
>> > >> linux-usb@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
>> > >> kernel@lists.infradead.org
>> > >> Subject: Re: [PATCH v3 2/3] USB3/DWC3: Add property "snps,
>> > >> incr-burst- type-adjustment" for INCR burst type
>> > >>
>> > >> On Mon, Dec 19, 2016 at 05:25:53PM +0800, Changming Huang wrote:
>> > >> > New property "snps,incr-burst-type-adjustment = <x>, <y>" for
>> > >> > USB3.0
>> > >> DWC3.
>> > >> > Field "x": 1/0 - undefined length INCR burst type enable or not;
>> > >> > Field
>> > >> > "y": INCR4/INCR8/INCR16/INCR32/INCR64/INCR128/INCR256 burst
>> type.
>> > >> >
>> > >> > While enabling undefined length INCR burst type and INCR16 burst
>> > >> > type, get better write performance on NXP Layerscape platform:
>> > >> > around 3% improvement (from 364MB/s to 375MB/s).
>> > >> >
>> > >> > Signed-off-by: Changming Huang <jerry.huang@nxp.com>
>> > >> > ---
>> > >> > Changes in v3:
>> > >> >   - add new property for INCR burst in usb node.
>> > >> >
>> > >> >  Documentation/devicetree/bindings/usb/dwc3.txt |    5 +++++
>> > >> >  arch/arm/boot/dts/ls1021a.dtsi                 |    1 +
>> > >> >  arch/arm64/boot/dts/freescale/fsl-ls1043a.dtsi |    3 +++
>> > >> >  arch/arm64/boot/dts/freescale/fsl-ls2080a.dtsi |    2 ++
>> > >> >  4 files changed, 11 insertions(+)
>> > >> >
>> > >> > diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt
>> > >> > b/Documentation/devicetree/bindings/usb/dwc3.txt
>> > >> > index e3e6983..8c405a3 100644
>> > >> > --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>> > >> > +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>> > >> > @@ -55,6 +55,10 @@ Optional properties:
>> > >> >     fladj_30mhz_sdbnd signal is invalid or incorrect.
>> > >> >
>> > >> >   - <DEPRECATED> tx-fifo-resize: determines if the FIFO *has* to
>> > >> > be
>> > >> reallocated.
>> > >> > + - snps,incr-burst-type-adjustment: Value for INCR burst type of
>> > >> GSBUSCFG0
>> > >> > +   register, undefined length INCR burst type enable and INCRx type.
>> > >> > +   First field is for undefined length INCR burst type enable or not.
>> > >> > +   Second field is for largest INCRx type enabled.
>> > >>
>> > >> Why do you need the first field? Is the 2nd field used if the 1st is 0?
>> > >> If not, then just use the presence of the property to enable or not.
>> > > The first field is one switch.
>> > > When it is 1, means undefined length INCR burst type enabled, we can
>> > > use
>> > any length less than or equal to the largest-enabled burst length of
>> > INCR4/8/16/32/64/128/256.
>> > > When it is zero, means INCRx burst mode enabled, we can use one
>> > > fixed
>> > burst length of 1/4/8/16/32/64/128/256 byte.
>> > > So, the 2nd field is used if the 1st is 0, we need to select one
>> > > largest burst
>> > length the USB controller can support.
>> > > If we don't want to change the value of this register (use the
>> > > default value),
>> > we don't need to add this property to usb node.
>> >
>> > Just make this a single value with 0 meaning INCR and 4/8/16/etc being
>> INCRx.
>> Maybe, I didn't describe it clearly.
>> According to DWC3 spec, the value "0" of field INCRBrstEna means INCRx
>> burst mode, 1 means INCR burst mode.
>> Regardless of the value of INCRBrstEna [bit0], we need to modify the other
>> field bit[1,2,3,4,5,6,7] to one INCR burst type  for the platform supported.
>> Ad you mentioned, if we just use a single value with 0 meaning INCR and
>> 4/8/16/etc being INCRx.
>> I understand totally that when it is none-zero, we can use it for INCR burst
>> mode.
>> Then, when it is 0, how to select the INCRx value?
>> 
>> So, I think we still need two vaue to specify INCRBrstEna and INCRx burst
>> type.
> Hi, Balbi, 
> It seems there is no feedback for my comment, so these patches can be accepted?

probably not, we need to really understand what information we need so
it can be described properly. The last thing we want is unnecessary DT
properties.

It seems to me that we can extrapolate INCRBrstEna based on which burst
modes are enabled. If only 0 is passed, then that bit should be 1, if 0
and any other size is passed, then that bit should be 0, no?

-- 
balbi

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