linux-kernel - Re: [PATCH V22 07/22] mmc: core: Support UHS-II card control and access

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Message-ID: <CAK00qKD20R4a=2ptDrwsoNA1jRRcpEyi5REKTuW-7EupDp=VKw@mail.gmail.com>
Date: Fri, 18 Oct 2024 18:39:34 +0800
From: Victor Shih <victorshihgli@...il.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: adrian.hunter@...el.com, linux-mmc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, benchuanggli@...il.com, 
	Lucas.Lai@...esyslogic.com.tw, HL.Liu@...esyslogic.com.tw, 
	Greg.tu@...esyslogic.com.tw, dlunev@...omium.org, 
	Jason Lai <jason.lai@...esyslogic.com.tw>, 
	Victor Shih <victor.shih@...esyslogic.com.tw>
Subject: Re: [PATCH V22 07/22] mmc: core: Support UHS-II card control and access

On Thu, Oct 10, 2024 at 7:22 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> [...]
>
> > > > +
> > > > +       /*
> > > > +        * NOTE:
> > > > +        * Should we read Externsion Register to check power notification feature here?
> > > > +        */
> > >
> > > Yes, this is needed too.
> > >
> >
> > Hi, Ulf
> >
> > We have the call sd_can_poweroff_notify() in the _mmc_sd_suspend() and
> > _sd_uhs2_suspend.
> > If we need to check the power notification feature here,
> > do you have any suggestions for the type of power notification that
> > needs to be confirmed?
>
> Right, I see what you mean! It's been a while since I read these parts
> of the SD spec, apologize for my ignorance.
>
> In UHS-II mode, the power-off-notification is *not* supported. This
> means that we should not use it from _sd_uhs2_suspend().
>
> In UHS-II mode we should instead use the so-called "hibernate" mode
> (hbr bit in the GO_DORMANT command), which allows us to turn off
> clocks and VDD1 (corresponds to the vmmc regulator). Note that the
> support for hibernate mode is optional for an UHS-II SD card. Thus,
> the support must be checked via the corresponding field in the PHY
> capabilities, before we try to use it.
>
> That said, to not make it more complicated for you to get the basic
> UHS-II support landed upstream, I am fine if you decide to defer the
> support for hibernate mode to later. Instead, it seems like we should
> just do a regular power-off in _sd_uhs2_suspend(). In other words,
> just call sd_uhs2_power_off() from there.
>
> Moreover, reading the SD Extension Registers would still be valuable
> during the UHS-II card initialization (even if hibernate isn't
> supported), as it allows us to support the "cache maintenance"
> feature, for example. However, the support for these features are
> optional too for SD cards, so I am fine if you decide to defer this to
> a later improvement too.
>
> Does this make sense to you?
>
> [...]
>
> Kind regards
> Uffe

Hi, Ulf

I hope that this feature can be implemented later.

Thanks, Victor Shih