Re: [PATCH] mmc: sdhci-pci-gli: Set SDR104's clock to 205MHz and enable SSC for GL975x

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Oct 14, 2020 at 04:00:49PM +0800, Ben Chuang wrote:
> Hi Greg,
> 
> On Tue, Oct 13, 2020 at 9:48 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Tue, Oct 13, 2020 at 07:11:13PM +0800, Ben Chuang wrote:
> > > On Tue, Oct 13, 2020 at 4:57 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Tue, Oct 13, 2020 at 04:33:38PM +0800, Ben Chuang wrote:
> > > > > On Tue, Oct 13, 2020 at 4:00 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > > > >
> > > > > > On Tue, Oct 13, 2020 at 03:46:00PM +0800, Ben Chuang wrote:
> > > > > > > From: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > > > > > >
> > > > > > > commit 786d33c887e15061ff95942db68fe5c6ca98e5fc upstream.
> > > > > > >
> > > > > > > Set SDR104's clock to 205MHz and enable SSC for GL9750 and GL9755
> > > > > > >
> > > > > > > Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
> > > > > > > Link: https://lore.kernel.org/r/20200717033350.13006-1-benchuanggli@gmail.com
> > > > > > > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> > > > > > > Cc: <stable@vger.kernel.org> # 5.4.x
> > > > > > > ---
> > > > > > > Hi Greg and Sasha,
> > > > > > >
> > > > > > > The patch is to improve the EMI of the hardware.
> > > > > > > So it should be also required for some hardware devices using the v5.4.
> > > > > > > Please tell me if have other questions.
> > > > > >
> > > > > > This looks like a "add support for new hardware" type of patch, right?
> > > > >
> > > > > No, this is for a mass production hardware.
> > > >
> > > > That does not make sense, sorry.
> > > >
> > > > Is this a bug that is being fixed, did the hardware work properly before
> > > > 5.4 and now it does not?  Or has it never worked properly and 5.9 is the
> > > > first kernel that it now works on?
> > >
> > > It seems there is misunderstanding regarding “hardware” means.
> > > I originally thought that the "hardware" refers to GL975x chips.
> > >
> > > This Genesys patch is to fix the EMI problem for GL975x controller on a system.
> >
> > Did it work on the 4.19 kernel?  Another older kernel?  Or is 5.9 the
> > first kernel release where it works?
> 
> The patch works on after v5.4.

You are not answering the question I am trying to ask.

My question is:
	Did this hardware ever work properly before the 5.9 kernel
	release.

> > In other words, is this fixing a regression, or just enabling hardware
> > support for something that has never worked before for this hardware?
> 
> This patch is to reduce the EMI at SDR104 mode for GL975x.
> It changes the preset frequency of SDR104 to 205Mhz and sets the SSC value.
> So I think it is fixing a regression.

A regression is when an older kernel works fine, but a newer kernel does
not.  When that happens, you can point to a specific commit and say,
"this commit here broke this previously working hardware".

Is that the case here?  If not, this is not a regression.

thanks,

greg k-h