| Message ID | 20190522071227.31488-3-andrew.smirnov@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/3] ARM: dts: imx6: rdu2: Add node for UCS1002 USB charger chip | expand |
Hi Andrey, Am Mittwoch, den 22.05.2019, 00:12 -0700 schrieb Andrey Smirnov: > Cabling used to connect devices to USBH1 on RDU2 does not meet USB > spec cable quality and cable length requirements to operate at High > Speed, so limit the port to Full Speed only. Really? I thought this issue is specific to the RDU1, but you've been looking at this USB stuff for a lot longer than me. Regards, Lucas > Reported-by: Chris Healy <cphealy@gmail.com> > Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com> > Cc: Shawn Guo <shawnguo@kernel.org> > Cc: Fabio Estevam <festevam@gmail.com> > Cc: Lucas Stach <l.stach@pengutronix.de> > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > --- > arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi > b/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi > index 5484e4b87975..3b37fe68d373 100644 > --- a/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi > +++ b/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi > @@ -772,6 +772,7 @@ > &usbh1 { > vbus-supply = <®_5p0v_main>; > disable-over-current; > + maximum-speed = "full-speed"; > status = "okay"; > }; >
On Wed, May 22, 2019 at 2:33 AM Lucas Stach <l.stach@pengutronix.de> wrote: > > Hi Andrey, > > Am Mittwoch, den 22.05.2019, 00:12 -0700 schrieb Andrey Smirnov: > > Cabling used to connect devices to USBH1 on RDU2 does not meet USB > > spec cable quality and cable length requirements to operate at High > > Speed, so limit the port to Full Speed only. > > Really? I thought this issue is specific to the RDU1, but you've been > looking at this USB stuff for a lot longer than me. > I am merely a messenger here. I didn't personally verify this to be the case, so your knowledge is probably as good as mine. Chris reported this based on feedback from their EE team, so he should know all of the details better. Thanks, Andrey Smirnov
> > Am Mittwoch, den 22.05.2019, 00:12 -0700 schrieb Andrey Smirnov: > > > Cabling used to connect devices to USBH1 on RDU2 does not meet USB > > > spec cable quality and cable length requirements to operate at High > > > Speed, so limit the port to Full Speed only. > > > > Really? I thought this issue is specific to the RDU1, but you've been > > looking at this USB stuff for a lot longer than me. > > > > I am merely a messenger here. I didn't personally verify this to be > the case, so your knowledge is probably as good as mine. Chris > reported this based on feedback from their EE team, so he should know > all of the details better. The issue is less about the internals of the device and more about the cabling that the device is connected to. In the target application of this device, the USB cables are almost always longer than the spec limit of the USB standard for high speed. Given our use cases, we don't have need for high speed so limiting the max speed to full speed is the way we work around cables that are too long for stable high speed operation. We have validated that running with full speed does mitigate the problems experienced when attempting to run with high speed on the target application installations. Reviewed-by: Chris Healy <cphealy@gmail.com>
diff --git a/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi b/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi index 5484e4b87975..3b37fe68d373 100644 --- a/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi +++ b/arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi @@ -772,6 +772,7 @@ &usbh1 { vbus-supply = <®_5p0v_main>; disable-over-current; + maximum-speed = "full-speed"; status = "okay"; };
Cabling used to connect devices to USBH1 on RDU2 does not meet USB spec cable quality and cable length requirements to operate at High Speed, so limit the port to Full Speed only. Reported-by: Chris Healy <cphealy@gmail.com> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com> Cc: Shawn Guo <shawnguo@kernel.org> Cc: Fabio Estevam <festevam@gmail.com> Cc: Lucas Stach <l.stach@pengutronix.de> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org --- arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi | 1 + 1 file changed, 1 insertion(+)