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

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Date:   Sun, 3 Mar 2019 23:03:29 +0900
From:   Katsuhiro Suzuki <katsuhiro@...suster.net>
To:     Heiko Stuebner <heiko@...ech.de>,
        Akash Gajjar <Akash_Gajjar@...tor.com>,
        Brian Norris <briannorris@...omium.org>,
        Christoph Muellner <christoph.muellner@...obroma-systems.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Jakob Unterwurzacher <jakob.unterwurzacher@...obroma-systems.com>,
        Klaus Goger <klaus.goger@...obroma-systems.com>,
        Levin Du <djw@...hip.com.cn>,
        Linus Walleij <linus.walleij@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Oskari Lemmela <oskari@...mela.net>,
        Robin Murphy <robin.murphy@....com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Shohei Maruyama <cheat.sc.linux@...look.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Vicente Bergas <vicencb@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2

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.

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>;
>>   			};
>>   		};
>>   
>>
> 
> 
> 
> 
> 
>