Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2

[Tony McKahan]

On Sun, Mar 3, 2019 at 2:51 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> On 2019-03-03 6:45 pm, Tony McKahan wrote:
> > Hello Katsushiro,
> >
> > On Sun, Mar 3, 2019 at 12:31 PM Katsuhiro Suzuki
> > <katsuhiro@xxxxxxxxxxxxx> wrote:
> >>
> >> Hello Tony,
> >>
> >> On 2019/03/04 0:13, Tony McKahan wrote:
> >>> On Sun, Mar 3, 2019 at 9:04 AM Katsuhiro Suzuki <katsuhiro@xxxxxxxxxxxxx> wrote:
> >>>>
> >>>> Hello Heiko,
> >>>>
> >>>> Thank you for comments.
> >>>>
> >>>> On 2019/03/03 22:19, Heiko Stuebner wrote:
> >>>>> Hi,
> >>>>>
> >>>>> Am Sonntag, 3. MÃrz 2019, 13:27:05 CET schrieb Katsuhiro Suzuki:
> >>>>>> This patch increases drive strength of UART2 from 3mA to 12mA for
> >>>>>> getting more faster rising edge.
> >>>>>>
> >>>>>> RockPro64 is using a very high speed rate (1.5Mbps) for UART2. In
> >>>>>> this setting, a bit width of UART is about 667ns.
> >>>>>>
> >>>>>> In my environment (RockPro64 UART2 with FTDI FT232RL UART-USB
> >>>>>> converter), falling time of RockPro64 UART2 is 40ns, but riging time
> >>>>>> is over 650ns. So UART receiver will get wrong data, because receiver
> >>>>>> read intermediate data of rising edge.
> >>>>>>
> >>>>>> Rising time becomes 300ns from 650ns if apply this patch. This is not
> >>>>>> perfect solution but better than now.
> >>>>>>
> >>>>>> Signed-off-by: Katsuhiro Suzuki <katsuhiro@xxxxxxxxxxxxx>
> >>>>>> ---
> >>>>>>     arch/arm64/boot/dts/rockchip/rk3399.dtsi | 9 +++++++--
> >>>>>>     1 file changed, 7 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> your changing a core rk3399 property here, so I'd really like to get
> >>>>> input from other board stakeholders on this before applying a core
> >>>>> change.
> >>>>>
> >>>>> Could you either include the submitters of other rk3399-boards in the
> >>>>> recipient list so that they're aware or limit the change to rockpro64 for
> >>>>> the time being (aka overriding the property in the board-dts) please?
> >>>>>
> >>>>
> >>>> OK, I'm adding other boards members.
> >>>> by ./scripts/get_maintainer.pl arch/arm64/boot/dts/rockchip/rk3399-*.dts
> >>>>
> >>>>
> >>>> RockPro64 directly connect UART2 pins of RK3399 to external connector.
> >>>> I think maybe other RK3399 boards are facing same problem, but I cannot
> >>>> check it because I have RockPro64 only...
> >>>>
> >>>> I'm happy if someone tell me other boards situation.
> >>>
> >>> I'm pulling out other rockchip boards momentarily to see what kind of
> >>> population we have.
> >>>
> >>> Note these are not all running 5.x kernels, however none of them have
> >>> the UART2 drive levels modified to my knowledge, and regardless, none
> >>> show over 100 ns.
> >>>
> >>> board:    rise/fall
> >>>
> >>> rk3399-roc-pc: 90ns/90ns
> >>> rk3399-rockpro64 V2.0:  90ns/45ns
> >>> rk3399-rockpro64 V2.1:  40ns/41ns
>
> I'm having to eyeball off a 20MHz analog scope (thank goodness for "yes"
> being able to generate a nice periodic signal), but for my NanoPC-T4
> with a cheap eBay FT232R adapter both rise and fall times are certainly
> <100ns. FWIW I've not noticed any issues with letting the Bluetooth
> interface on UART0 run flat-out at 4Mbaud either.
>
> >>>
> >>> Please make sure there's not a large amount of flux or something
> >>> around the terminals on your board, that seems excessively high.
> >>>
> >>
> >> Thank you for valuable information. For more deeply discussion,
> >> I tried other conditions and watch the rise/fall times.
> >>
> >> 1) Not connect
> >> The rise/fall times are 40ns/5ns when nothing connect (impedance is
> >> very high) to external pin of RockPro64.
> >>
> >> What UART device are you using with RockPro64? If you use some device
> >> with RockPro64 and board shows rise/fall times = 90ns/45ns, my device
> >> is not suitable for RockPro64 by some reason. So it's better to drop
> >> my patch.
> >
> > The adapter is an FTDI FT232RL breakout board, attached with some
> > generic Dupont connector jumpers.
> > Interesting your RockPro is showing this symptom, perhaps there is a
> > cold solder joint somewhere introducing resistance?
> >
> >>
> >> 2) Other SoC
> >> I have other SoC board rk3328-rock64, Rock64 shows rise/fall times =
> >> 90ns/80ns when same UART-USB device is connected to UART pin.
> >
> > I measured similar on my Rock64 as well.
> >
> >>
> >> I think it shows rk3399's (or RockPro64's?) drive strength is a little
> >> weak. So it's better to increase the drive strength of UART of rk3399.
> >
> > I do not think this is a bad idea generally, it simply allows for more
> > available current from the interface.  I'll let others be the judge of
> > that, however.
>
> There may be RK3399 users who would care about the possible EMI impact,
> so it's probably still best to limit such a change to boards which
> definitely need it.
>

Ah, good point.

As to speeds achievable, I've only run into drive level issues with
SD/SDIO, but that's all the way up at 25-50 MHz.

Tony

> Robin.
>
> >
> >>
> >> Best Regards,
> >> Katsuhiro Suzuki
> >>
> >>>>
> >>>> Best Regards,
> >>>> Katsuhiro Suzuki
> >>>>
> >>>>
> >>>>> Thanks
> >>>>> Heiko
> >>>>>
> >>>>>
> >>>>>
> >>>>>> diff --git a/arch/arm64/boot/dts/rockchip/rk3399.dtsi b/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> >>>>>> index beaa92744a64..e3c8f91ead50 100644
> >>>>>> --- a/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> >>>>>> +++ b/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> >>>>>> @@ -2000,6 +2000,11 @@
> >>>>>>                        drive-strength = <8>;
> >>>>>>                };
> >>>>>>
> >>>>>> +            pcfg_pull_up_12ma: pcfg-pull-up-12ma {
> >>>>>> +                    bias-pull-up;
> >>>>>> +                    drive-strength = <12>;
> >>>>>> +            };
> >>>>>> +
> >>>>>>                pcfg_pull_up_18ma: pcfg-pull-up-18ma {
> >>>>>>                        bias-pull-up;
> >>>>>>                        drive-strength = <18>;
> >>>>>> @@ -2521,8 +2526,8 @@
> >>>>>>                uart2c {
> >>>>>>                        uart2c_xfer: uart2c-xfer {
> >>>>>>                                rockchip,pins =
> >>>>>> -                                    <4 RK_PC3 RK_FUNC_1 &pcfg_pull_up>,
> >>>>>> -                                    <4 RK_PC4 RK_FUNC_1 &pcfg_pull_none>;
> >>>>>> +                                    <4 RK_PC3 RK_FUNC_1 &pcfg_pull_up_12ma>,
> >>>>>> +                                    <4 RK_PC4 RK_FUNC_1 &pcfg_pull_none_12ma>;
> >>>>>>                        };
> >>>>>>                };
> >>>>>>
> >>>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> Linux-rockchip mailing list
> >>>> Linux-rockchip@xxxxxxxxxxxxxxxxxxx
> >>>> http://lists.infradead.org/mailman/listinfo/linux-rockchip
> >>>
> >>>
> >>