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

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Date:   Tue, 17 Jan 2017 11:08:57 +0000
From:   Jerry Huang <jerry.huang@....com>
To:     Felipe Balbi <balbi@...nel.org>, Rob Herring <robh@...nel.org>
CC:     "mark.rutland@....com" <mark.rutland@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v3 2/3] USB3/DWC3: Add property "snps,
 incr-burst-type-adjustment" for INCR burst type


> -----Original Message-----
> From: Felipe Balbi [mailto:balbi@...nel.org]
> Sent: Tuesday, January 17, 2017 6:45 PM
> To: Jerry Huang <jerry.huang@....com>; Rob Herring <robh@...nel.org>
> Cc: mark.rutland@....com; catalin.marinas@....com;
> will.deacon@....com; linux@...linux.org.uk; devicetree@...r.kernel.org;
> linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org
> Subject: RE: [PATCH v3 2/3] USB3/DWC3: Add property "snps, incr-burst-
> type-adjustment" for INCR burst type
> 
> 
> Hi,
> 
> Jerry Huang <jerry.huang@....com> writes:
> 
> <snip>
> 
> >> >> 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?
> > Hi, Balbi,
> > Below is the definition for this property,
> > snps,incr-burst-type-adjustment = <x>, <y>
> > x: Undefined Length INCR Burst Type Enable (INCRBrstEna)
> >     0 - INCRX burst mode (not enable INCRBrstEna)
> >     1 - INCR (undefined length) burst mode (enable INCRBrstEna)
> > y: the burst length
> >
> > 1> if x = 0: means INCRBrstEna not enabled, set bit0 to zero (or clear
> > it) , we select one of
> > INCR1/INCR4/INCR8/INCR16/INCR32/INCR64/INCR128/INCR256 (pass this
> > value through "y")to set the fix burst length controller supported.
> >
> > For example:
> >
> > 	snps,incr-burst-type-adjustment = <0>, <16>
> >
> > driver will set bit0 to zero and set bit3 to 1 (INCR16 Burst Type
> > Enabled), controller will use INCR16 (with 16 bytes) to transfer data.
> >
> > 2> if x = 1: means INCRBrstEna enabled, we select one of
> > INCR4/INCR8/INCR16/INCR32/INCR64/INCR128/INCR256 (pass this value
> > through "y") to set the burst length, and controller will use any
> > length less than or equal to that we selected.
> >
> > For example:
> >
> > 	snps,incr-burst-type-adjustment = <1>, <32>
> >
> > driver will set bit0 to 1 and set bit4 to 1 (INCR32 Burst Type
> > Enabled), controller will use any burst length less than (such as 4,
> > 8, 16 byte) or equal to 32 byte to transfer data.
> >
> > Therefore, I think this two fileds are needed. Do you think about it?
> 
> no, I don't think two values are needed, because first value can be
> extrapolated from the second. Something like this:
> 
> 	snps,incr-burst-type-adjustment = <4>, <8>, <16>, <32>;
> 
> This is basically telling us that we can support anything in this list. So
> INCRBrstEna should be set to 1.
> 
> If DT, on the other hand, says:
> 
> 	snps,incr-burst-type-adjustment = <32>;
> 
> this means that we can only support INCR32, so INCRBrstEna should be
> cleared to 0.
Got it, I will try this mode.
Thanks a lot, Balbi,