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

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Message-ID: <787c804009c74f478675e7257b4858c7@realtek.com>
Date:   Thu, 24 Feb 2022 05:49:52 +0000
From:   Ricky WU <ricky_wu@...ltek.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
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

> -----Original Message-----
> From: gregkh@...uxfoundation.org <gregkh@...uxfoundation.org>
> Sent: Tuesday, February 22, 2022 10:18 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 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?
> 

spec original is
"Host provides at least 74 Clocks before issuing first command"
Let me clarify it, 
74 Clocks means 74 clock signals, our Card Reader need to issue more than 74 Clock signals to Card before first command
So mdelay(5) , our device will keep issue signal to card in this 5ms make sure over 74 

> thanks,
> 
> greg k-h
> ------Please consider the environment before printing this e-mail.