linux-kernel - Re: [PATCH] mmc: rtsx: add 74 Clocks in power on flow

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Message-ID: <YhTwm9yDEhjEXt6H@kroah.com>
Date:   Tue, 22 Feb 2022 15:18:03 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Ricky WU <ricky_wu@...ltek.com>
Cc:     "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "kai.heng.feng@...onical.com" <kai.heng.feng@...onical.com>,
        "tommyhebb@...il.com" <tommyhebb@...il.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: rtsx: add 74 Clocks in power on flow

On Tue, Feb 22, 2022 at 12:31:10PM +0000, Ricky WU wrote:
> > -----Original Message-----
> > From: gregkh@...uxfoundation.org <gregkh@...uxfoundation.org>
> > Sent: Tuesday, February 22, 2022 4:59 PM
> > To: Ricky WU <ricky_wu@...ltek.com>
> > Cc: ulf.hansson@...aro.org; kai.heng.feng@...onical.com;
> > tommyhebb@...il.com; linux-mmc@...r.kernel.org;
> > linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] mmc: rtsx: add 74 Clocks in power on flow
> > 
> > On Tue, Feb 22, 2022 at 08:48:30AM +0000, Ricky WU wrote:
> > > > -----Original Message-----
> > > > From: gregkh@...uxfoundation.org <gregkh@...uxfoundation.org>
> > > > Sent: Tuesday, February 22, 2022 3:42 PM
> > > > To: Ricky WU <ricky_wu@...ltek.com>
> > > > Cc: ulf.hansson@...aro.org; kai.heng.feng@...onical.com;
> > > > tommyhebb@...il.com; linux-mmc@...r.kernel.org;
> > > > linux-kernel@...r.kernel.org
> > > > Subject: Re: [PATCH] mmc: rtsx: add 74 Clocks in power on flow
> > > >
> > > > On Tue, Feb 22, 2022 at 07:27:52AM +0000, Ricky WU wrote:
> > > > > After 1ms stabilizing the voltage time add "Host provides at least
> > > > > 74 Clocks before issuing first command" that is spec definition
> > > >
> > > > You do have 72 columns to use here, no need to wrap this so tightly.
> > > >
> > >
> > > Ok...
> > > so I need to have next patch to fix this format?
> > 
> > Please do, because:
> > 
> > >
> > > > >
> > > > > Signed-off-by: Ricky Wu <ricky_wu@...ltek.com>
> > > > > ---
> > > > >  drivers/mmc/host/rtsx_pci_sdmmc.c | 7 +++++++
> > > > >  1 file changed, 7 insertions(+)
> > > > >
> > > > > diff --git a/drivers/mmc/host/rtsx_pci_sdmmc.c
> > > > > b/drivers/mmc/host/rtsx_pci_sdmmc.c
> > > > > index 2a3f14afe9f8..e016d720e453 100644
> > > > > --- a/drivers/mmc/host/rtsx_pci_sdmmc.c
> > > > > +++ b/drivers/mmc/host/rtsx_pci_sdmmc.c
> > > > > @@ -940,10 +940,17 @@ static int sd_power_on(struct
> > > > > realtek_pci_sdmmc
> > > > *host)
> > > > >  	if (err < 0)
> > > > >  		return err;
> > > > >
> > > > > +	mdelay(1);
> > > >
> > > > What is this delay for?
> > > >
> > >
> > > Spec definition, need to wait 1ms for voltage stable and below
> > > mdelay(5) is our device send 74 Clocks time
> > 
> > Clock cycles and mdelay() are not going to always stay the same, right?
> > 
> > I really have no idea what "74 clocks time" means, is this some specific timing
> > value for this hardware?  What is the units?  This needs to be documented
> > better in both the changelog and in the code.
> > 
> > thanks,
> > 
> 
> Please ref: https://www.sdcard.org/downloads/pls/ Version8

I can not download those specifications according to the license that
they ask me to abide by.

> And see the 6.4.1.2 Power Up Time of Host Figure 6-5: Power Up Diagram of Host
> mdelay(1) corresponds to Stable supply voltage
> mdelay(5) corresponds to Host provides at least 74 Clocks before issuing first command
> our device need 5ms to issue 74 Clocks

What is a "clock"?  The kernel works with time units, how does "5" equal
to 74?

thanks,

greg k-h