linux-kernel - Re: [PATCH 2/2] usb: typec: add support for the nb7vpq904m Type-C Linear Redriver

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Date:   Mon, 5 Jun 2023 10:31:36 +0200
From:   neil.armstrong@...aro.org
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] usb: typec: add support for the nb7vpq904m Type-C
 Linear Redriver

Hi,

On 05/06/2023 10:24, Heikki Krogerus wrote:
> Hi Neil,
> 
> On Thu, Jun 01, 2023 at 11:21:13AM +0200, neil.armstrong@...aro.org wrote:
>> From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>
>> Add support for the ON Semiconductor NB7VPQ904M Type-C USB SuperSpeed
>> and DisplayPort ALT Mode Linear Redriver chip found on some devices
>> with a Type-C port.
>>
>> The redriver compensates ultra High-Speeed DisplayPort and USB
>> Super Speed signal integrity losses mainly due to PCB & transmission
>> cables.
>>
>> The redriver doesn't support SuperSpeed lines swapping, but
>> can support Type-C SBU lines swapping.
>>
>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>> ---
>>   drivers/usb/typec/mux/Kconfig      |   8 +
>>   drivers/usb/typec/mux/Makefile     |   1 +
>>   drivers/usb/typec/mux/nb7vpq904m.c | 526 +++++++++++++++++++++++++++++++++++++
>>   3 files changed, 535 insertions(+)
> 
> This looks good to me, but I think you should register a retimer
> instead of a mode switch (the orientation switch is fine).

Indeed, I'm not familiar with namings but by looking around it seems that
redriver and retimers for USB-C applications are exactly the same.

> 
> Retimers are handled just like the muxes, so this patch would not need
> that many changes, but you would need to change the first patch too.
> You would need to declare a "redriver-switch" instead of "mode-switch"
> property in your DT (or perhaps make it just "redriver" instead of
> "redriver-switch"?).

So it would need some additional handling to also set the retimer state
along the mux, but I was wondering, why having a separate handling
while the retimer state struct is exactly the same as the mux ?

> 
> We just need to add a device type for redrivers to the retimer class -
> check the attached diff. Something like that.
> 
> Let me know what you guys think.

I think I'll switch to retimer, thanks for pointing it to me...

Thanks,
Neil

> 
> thanks,
>