Messages in this thread Patch in this message | | | Subject | Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2 | From | Robin Murphy <> | Date | Sun, 3 Mar 2019 19:50:49 +0000 |
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On 2019-03-03 6:45 pm, Tony McKahan wrote: > Hello Katsushiro, > > On Sun, Mar 3, 2019 at 12:31 PM Katsuhiro Suzuki > <katsuhiro@katsuster.net> wrote: >> >> Hello Tony, >> >> On 2019/03/04 0:13, Tony McKahan wrote: >>> On Sun, Mar 3, 2019 at 9:04 AM Katsuhiro Suzuki <katsuhiro@katsuster.net> wrote: >>>> >>>> Hello Heiko, >>>> >>>> Thank you for comments. >>>> >>>> On 2019/03/03 22:19, Heiko Stuebner wrote: >>>>> Hi, >>>>> >>>>> Am Sonntag, 3. März 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@katsuster.net> >>>>>> --- >>>>>> 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.
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@lists.infradead.org >>>> http://lists.infradead.org/mailman/listinfo/linux-rockchip >>> >>> >>
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