Re: GPMI iMX6ull timeout on DMA

From: Michael Nazzareno Trimarchi <michael@amarulasolutions.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: "Christian Eggers" <ceggers@arri.de>,
	"Stefan Riedmüller" <S.Riedmueller@phytec.de>,
	"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
	"han.xu@nxp.com" <han.xu@nxp.com>,
	"Christian Hemp" <C.Hemp@phytec.de>,
	"gerg@kernel.org" <gerg@kernel.org>,
	"linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>
Subject: Re: GPMI iMX6ull timeout on DMA
Date: Sat, 9 Oct 2021 07:53:26 +0200	[thread overview]
Message-ID: <CAOf5uwkTzPtqjO0XQ7otzNKLugUzS+9MJg0GkdtvV2JY4=n5mw@mail.gmail.com> (raw)
In-Reply-To: <20211008180752.09f33896@xps13>

Hi

On Fri, Oct 8, 2021 at 6:07 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Christian,
>
> ceggers@arri.de wrote on Fri, 8 Oct 2021 15:49:21 +0200:
>
> > On Friday, 8 October 2021, 15:36:31 CEST, Miquel Raynal wrote:
> > >
> > > miquel.raynal@bootlin.com wrote on Fri, 8 Oct 2021 15:29:05 +0200:
> > >
> > > >
> > > > If this clock (as I understand) does not prevent us to access the
> > > > registers but only feeds the external NAND bus part, then there is no
> > > > need to enable it in the probe, just acquiring it will be enough.
> >
> > clocks[0] is "gpmi_io" which sounds more like i/o than registers. So lets
> > try to remove the initial call to clk_set_rate().
> >
> > > > Then, the first call for an IO operation with ->must_apply_timings
> > > > should:
> > > >
> > > >   if (imx6)
> > > >           disable_clk();
> > > >
> > > >   clk_set_rate();
> > > >
> > > >   if (imx6)
> > > >           enable_clk();
> >
> > Do you think that the need for avoiding clock glitches is i.MX6 specific?
> > The errata I mentioned is specific for the bootloader software, but (I think)
> > the requirement for switching off the clocks gates prior changing the dividers
> > may apply also for other series.
>
> I honestly don't know, perhaps Han have more details about it. If you
> think it's a wider issue, then we can just do the disable/enable step
> without any further checks.
>

Still don't explain why it was working on the old driver. The glitch
was already there,
so just a delay can do the trick. For imx28 we need to reparent to a
different clock the
nand driver in order to get the frequency we want in EDO mode. I'm
still thinking that
set the frequency without without get back and understand if in that
edo mode is valid
is still a bug.

Michael

> > > Actually we should ensure clks are enabled in the !imx6 case anyway,
> > > but this is needed only once so either we keep enabling the clock in
> > > the probe or we check here if the clk has already been enabled or not.
> > The clocks are already enabled (and kept on) in probe. The initial call to
> > clk_set_rate() is just above this (but the clocks are not disabled at this
> > stage as all gates have been enabled by the boot loader).
>
> The IO clock should be enabled and set to a particular rate the first
> time the die is selected to perform a NAND operation, or when we switch
> from one device to the other (this does not apply to the GPMI driver
> for now). So we can drop the enable/set_rate call in the probe if the
> assumption that this clock only feeds the external bus is right.
>
> Thanks,
> Miquèl

-- 
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@amarulasolutions.com
__________________________________

Amarula Solutions BV
Joop Geesinkweg 125, 1114 AB, Amsterdam, NL
T. +31 (0)85 111 9172
info@amarulasolutions.com
www.amarulasolutions.com

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/