linux-kernel - Re: [PATCH 2/2] phy: rockchip-emmc: try to get drive impedance from DT

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Message-ID: <669c85b1-f0fb-c58e-90a8-3aeac3118656@rock-chips.com>
Date:   Fri, 6 Jan 2017 09:09:53 +0800
From:   Shawn Lin <shawn.lin@...k-chips.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     shawn.lin@...k-chips.com, Kishon Vijay Abraham I <kishon@...com>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Heiko Stuebner <heiko@...ech.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] phy: rockchip-emmc: try to get drive impedance from
 DT

On 2017/1/6 8:51, Doug Anderson wrote:
> Hi,
>
> On Thu, Jan 5, 2017 at 1:31 AM, Shawn Lin <shawn.lin@...k-chips.com> wrote:
>> Try to get drive impedance from DT and use it, otherwise
>> use 50ohm by default in order not to break the existing boards
>> as 50ohm works fine for them already.
>>
>> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
>> ---
>>
>>  drivers/phy/phy-rockchip-emmc.c | 29 ++++++++++++++++++++++++++++-
>>  1 file changed, 28 insertions(+), 1 deletion(-)
>
> I could have sworn that you somehow needed to make sure that the eMMC
> part itself needed to also be updated to be told the matching drive
> impedance so you don't get a mismatch.  How do you make that work?

No I didn't. So that means the eMMC part itself still couldn't be
updated. The intention for me to introduce this only for emmc phy is
that I got report that the default drive impedance of one eMMC is not
50ohms, so now we haven't been able to update it for eMMC part but maybe
we could just update it for the phy itself to match them in between.


> ...or am I just confused.  I meant to try to dig more, but ran out of
> time today.  :(
>
> -Doug
>
>
>


-- 
Best Regards
Shawn Lin