On Fri, Aug 14, 2015 at 12:02:37PM +0200, Lucas Stach wrote: > Am Freitag, den 14.08.2015, 16:40 +0800 schrieb Peter Chen: > > On Fri, Aug 14, 2015 at 10:37:30AM +0200, Lucas Stach wrote: > > > Am Freitag, den 07.08.2015, 15:15 +0800 schrieb Peter Chen: > > > > It is used to override the default setting for burst size, changing > > > > burst size takes effect only when the SBUSCFG.AHBBRST = 0. > > > > > > > > Signed-off-by: Peter Chen <peter.chen@xxxxxxxxxxxxx> > > > > --- > > > > Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt | 10 ++++++++++ > > > > 1 file changed, 10 insertions(+) > > > > > > > > diff --git a/Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt b/Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt > > > > index d52a747..d71ef07 100644 > > > > --- a/Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt > > > > +++ b/Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt > > > > @@ -37,6 +37,14 @@ Optional properties: > > > > property is used to change AHB burst configuration, check the chipidea > > > > spec for meaning of each value. If this property is not existed, it > > > > will use the reset value. > > > > +- tx-burst-size-dword: it is vendor dependent, the tx burst size in dword > > > > + (4 bytes), This register represents the maximum length of a the burst > > > > + in 32-bit words while moving data from system memory to the USB > > > > + bus, changing this value takes effect only the SBUSCFG.AHBBRST is 0. > > > > > > The last bits about SBUSCFG.AHBBRST don't make any sense in the DT > > > binding. The DT writer doesn't know about the SBUSCFG.AHBBRST value and > > > should not care either. > > > If someone sets the burst size to something > > > non-standard in the DT, the driver should make sure to enable to > > > necessary bits to make this setting take effect. > > > > The SBUSCFG.AHBBRST property description is just above this one, > > and the user should read the spec for changing these system > > configuration parameters. > > > This is not clear from the description. This should read something like > "The value of this property will only take effect if property > ahb-burst-config is set to 0." Thanks, will change. > > The DT binding should be coherent and understandable without reading the > DW USB spec and/or the code. Please take some care about this. > > > This requirement is from the spec, and the code logic makes sure > > the burst size changes only when SBUSCFG.AHBBRST is 0, since the > > hardware will only change burst size if SBUSCFG.AHBBRST is 0. > > > > > > > > Also both those descriptions are missing a description to what value the > > > burst sizes will be set if the DT properties are not found. If it's > > > implementation defined spell this out in the doc. > > > > It is optional property, if without this property, it will use the > > default value. > > > Then specify this in the binding. Again, the binding is a spec that one > should be able to understand without reading the code. > > "If this property is missing the reset defaults of the hardware > implementation will be used." > Thanks, will change. > > > > > > Are there really cases where it makes sense to set RX and TX burst sizes > > > to different values? > > > > Yes, the default burst size is the same for all SoCs, but the bus > > burst size may be larger for some SoCs. > > > This question wasn't meant to dispute the RX/TX burst size > configuration, but I'm questioning if it really makes sense to set them > to different values. Do we really need 2 properties for this, or is 1 > enough? > > Do you see any use case where someone would like to do something like: > tx-burst-size-dword = <0x8>; > rx-burst-size-dword = <0x10>; > For Freelscae i.mx current design, the tx/rx burst size are always the same, but not sure if it is always true for others or for future design. -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
