linux-kernel - Re: [PATCH v2 1/2] dt-bindings: phy: mediatek,mt7988-xfi-tphy: add new bindings

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Date: Wed, 7 Feb 2024 16:07:09 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Daniel Golle <daniel@...rotopia.org>
Cc: SkyLake Huang <SkyLake.Huang@...iatek.com>,
 Bc-bocun Chen <bc-bocun.chen@...iatek.com>,
 Chunfeng Yun <chunfeng.yun@...iatek.com>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Matthias Brugger
 <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Qingfang Deng <dqfext@...il.com>, Philipp Zabel <p.zabel@...gutronix.de>,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org,
 linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: phy: mediatek,mt7988-xfi-tphy: add
 new bindings

On 06/02/2024 16:31, Daniel Golle wrote:
> Hi Krzysztof,
> 
> On Tue, Feb 06, 2024 at 11:53:55AM +0100, Krzysztof Kozlowski wrote:
>> On 05/02/2024 18:28, Daniel Golle wrote:
>>> Add bindings for the MediaTek XFI Ethernet SerDes T-PHY found in the
>>> MediaTek MT7988 SoC which can operate at various interfaces modes:
>>>
>>> via USXGMII PCS:
>>>  * USXGMII
>>>  * 10GBase-R
>>>  * 5GBase-R
>>>
>>> via LynxI SGMII PCS:
>>>  * 2500Base-X
>>>  * 1000Base-X
>>>  * Cisco SGMII (MAC side)
>>>
>>> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
>>> ---
>>> v2: unify filename and compatible as requested
>>
>> Several comments, from me and Rob, were ignored. Please respond to them.
> 
> I'm sorry if I have missed something. I just checked again on
> patchwork, just in case I would have missed an email reply to this or
> any of the preceding posts of this patch as part of the old series
> going to netdev.
> 
> Comments you have made which I have addressed:
>  - removed $nodename
>  - use compatible as filename
> 
> And the only thing I found that I didn't either fix or reply to is this:
>> Can you explain what is this issue and errata about (except performance)?
> 
> Not overwriting that (undocumented) value in that (undocumented)
> register results in 10GBase-R having performance issues according to a
> commit in MediaTek's SDK, see here:
> 
> https://git01.mediatek.com/plugins/gitiles/openwrt/feeds/mtk-openwrt-feeds/+/a500d94cd%5E%21/#F0
> 
> Maybe Bc or SkyLake of MediaTek (added to Cc) can explain this in more
> detail?
> 
> 
> What I did miss was Rob's comment at the very bottom of this reply:
>> What is PEXTP?
> 
> I can again only answer by referencing to MediaTek's SDK sources:
> 
> https://git01.mediatek.com/plugins/gitiles/openwrt/feeds/mtk-openwrt-feeds/+/refs/heads/master/21.02/files/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_sgmii.c#96
> 
> Here this reset is called XFI_PEXTP0_GRST.
> 
> I personally find that name confusing (as this PHY has nothing to do with
> _P_ci _EX_press) and have tried to get rid of it where it isn't either part
> of official documentation or already merged drivers (like Sam's clock driver).
> 
> If there have been any other issues with this patch which I'm not aware
> of, please point them out to me.

These both cases should be explained in the binding somehow.

Best regards,
Krzysztof