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Subject: Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2
To:     Tony McKahan <tonymckahan@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>
Cc:     Heiko Stuebner <heiko@sntech.de>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-kernel@vger.kernel.org,
        Klaus Goger <klaus.goger@theobroma-systems.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        Brian Norris <briannorris@chromium.org>,
        linux-rockchip@lists.infradead.org,
        Shawn Lin <shawn.lin@rock-chips.com>,
        Akash Gajjar <Akash_Gajjar@mentor.com>,
        Vicente Bergas <vicencb@gmail.com>,
        Levin Du <djw@t-chip.com.cn>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        linux-arm-kernel@lists.infradead.org,
        Shohei Maruyama <cheat.sc.linux@outlook.com>,
        Matthias Brugger <mbrugger@suse.com>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Douglas Anderson <dianders@chromium.org>,
        Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>,
        Oskari Lemmela <oskari@lemmela.net>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Christoph Muellner <christoph.muellner@theobroma-systems.com>
References: <20190303122705.27094-1-katsuhiro@katsuster.net>
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 <e722acb4-167f-8333-5c8a-b693815273f4@katsuster.net>
 <CAERgoknAV1sACSPjM_u4WyWzLvmUntXMoEx=ccpFsqYZVeu__Q@mail.gmail.com>
 <26c3aea3-959f-bfb3-177f-3e5314494361@katsuster.net>
 <CAERgoknMO6xMzuhCn2kSHZm8Pt+6YH3jDvJckJq28u9OW08u2Q@mail.gmail.com>
 <7ac5038b-ce5d-89d1-4eee-6864837272c6@arm.com>
 <CAERgokm-c50Py-m9Stu=8+7dnDryDR6A9pL-CYM_JkPD_XTj2w@mail.gmail.com>
From:   Katsuhiro Suzuki <katsuhiro@katsuster.net>
Message-ID: <b35a6d3d-d3af-de0b-1dc8-6849d86c7b71@katsuster.net>
Date:   Mon, 4 Mar 2019 22:59:46 +0900
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Hello Tony, Robin,

On 2019/03/04 5:41, Tony McKahan wrote:
> On Sun, Mar 3, 2019 at 2:51 PM Robin Murphy <robin.murphy@arm.com> 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@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.
>>

Robin, Thanks a lot. Your results show that cold solder (or some
electric parts on board) of my RockPro64 is broken or something wrong.


>>>>>
>>>>> 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.
>>>

Tony, thanks for your info about environment.

It seems my RockPro64 problem. I don't have enough electronic knowledge,
but try to check my RockPro64 as much as I can.


>>>>
>>>> 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.

My patch has bad effects for EMI issues of all RK3399 boards.

So conclusion is, my patch should be dropped. Sorry for confusing.

Best Regards,
Katsuhiro Suzuki


> 
> 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@lists.infradead.org
>>>>>> http://lists.infradead.org/mailman/listinfo/linux-rockchip
>>>>>
>>>>>
>>>>
> 
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