Date:   Tue, 26 Mar 2019 22:39:42 +0900
From:   Katsuhiro Suzuki <katsuhiro@...suster.net>
To:     Tony McKahan <tonymckahan@...il.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel@...r.kernel.org,
        Klaus Goger <klaus.goger@...obroma-systems.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Brian Norris <briannorris@...omium.org>,
        linux-rockchip@...ts.infradead.org,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Akash Gajjar <Akash_Gajjar@...tor.com>,
        Vicente Bergas <vicencb@...il.com>,
        Levin Du <djw@...hip.com.cn>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        linux-arm-kernel@...ts.infradead.org,
        Shohei Maruyama <cheat.sc.linux@...look.com>,
        Matthias Brugger <mbrugger@...e.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Jakob Unterwurzacher <jakob.unterwurzacher@...obroma-systems.com>,
        Oskari Lemmela <oskari@...mela.net>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Christoph Muellner <christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2

Hello Tony, Robin,

I continue to investigate UART TX rising time problem. Recently, I found
one of cause of this problem.

In my environment, this problem occurred on linux-next only. U-Boot does
not face it. So I compared settings between U-Boot and linux-next. After
I found GRF_IO_VSEL (address 0xff77e640) register is differ.


Would you tell me what value is stored into this register?


My RockPro64, initially 0x00000000 is set but 0x00000003 is set during
linux boot. UART TX rising time becomes fine if set both bit 1 and bit 3
or clear both bits.


Best Regards,


On 2019/03/04 22:59, Katsuhiro Suzuki wrote:
> 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@....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@...suster.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@...suster.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@...suster.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@...ts.infradead.org
>>>>>>> http://lists.infradead.org/mailman/listinfo/linux-rockchip
>>>>>>
>>>>>>
>>>>>
>>
>> _______________________________________________
>> Linux-rockchip mailing list
>> Linux-rockchip@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-rockchip
>>
>>
> 
> 

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