Re: [PATCH V4] clk: at91: PLL recalc_rate() now using cached MUL and DIV values

From: Marcin Ziemianowicz <marcin@ziemianowicz.com>
To: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH V4] clk: at91: PLL recalc_rate() now using cached MUL and DIV values
Date: Wed, 9 May 2018 00:32:05 -0400	[thread overview]
Message-ID: <20180509043205.GA57916@hak8or> (raw)
In-Reply-To: <20180430075847.29706679@bbrezillon>

On Mon, Apr 30, 2018 at 07:58:47AM +0200, Boris Brezillon wrote:
> On Sun, 29 Apr 2018 15:01:11 -0400
> Marcin Ziemianowicz <marcin@ziemianowicz.com> wrote:
> 
> > When a USB device is connected to the USB host port on the SAM9N12 then
> > you get "-62" error which seems to indicate USB replies from the device
> > are timing out. Based on a logic sniffer, I saw the USB bus was running
> > at half speed.
> > 
> > The PLL code uses cached MUL and DIV values which get set in set_rate()
> > and applied in prepare(), but the recalc_rate() function instead
> > queries the hardware instead of using these cached values. Therefore,
> > if recalc_rate() is called between a set_rate() and prepare(), the
> > wrong frequency is calculated and later the USB clock divider for the
> > SAM9N12 SOC will be configured for an incorrect clock.
> > 
> > In my case, the PLL hardware was set to 96 Mhz before the OHCI
> > driver loads, and therefore the usb clock divider was being set
> > to /2 even though the OHCI driver set the PLL to 48 Mhz.
> > 
> > As an alternative explanation, I noticed this was fixed in the past by
> > 87e2ed338f1b ("clk: at91: fix recalc_rate implementation of PLL
> > driver") but the bug was later re-introduced by 1bdf02326b71 ("clk:
> > at91: make use of syscon/regmap internally").
> > 
> > Fixes: 1bdf02326b71 ("clk: at91: make use of syscon/regmap internally)
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Marcin Ziemianowicz <marcin@ziemianowicz.com>
> 
> Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>

Apologies for being a bother, but since it's been a bit over a week,
should I do something with this now that it has been ACK'd? I was thinking
I would see it somewhere on the git group repo but am not seeing it there
yet. Googling says that there is a "review cycle" for some maintainers, but
I am not clear on if I need to initiate it manually or anything of the sort.

https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git/ 

> 
> > ---
> > Thank you for bearing with me about this Boris.
> > 
> > Changes since V3:
> >   Fix for double returns found by kbluild test robot
> >   > Comments by Boris Brezillon about email formatting issues  
> > Changes since V2:
> >   Removed all logging/debug messages I added
> >   > Comment by Boris Brezillon about my fix being wrong addressed  
> > Changes since V1:
> >   Added patch set cover letter
> >   Shortened lines which were over >80 characters long
> >   > Comment by Greg Kroah-Hartman about "from" field in email addressed
> >   > Comment by Alan Stern about redundant debug lines addressed  
> > 
> >  drivers/clk/at91/clk-pll.c | 13 +------------
> >  1 file changed, 1 insertion(+), 12 deletions(-)
> > 
> > diff --git a/drivers/clk/at91/clk-pll.c b/drivers/clk/at91/clk-pll.c
> > index 7d3223fc..72b6091e 100644
> > --- a/drivers/clk/at91/clk-pll.c
> > +++ b/drivers/clk/at91/clk-pll.c
> > @@ -132,19 +132,8 @@ static unsigned long clk_pll_recalc_rate(struct clk_hw *hw,
> >  					 unsigned long parent_rate)
> >  {
> >  	struct clk_pll *pll = to_clk_pll(hw);
> > -	unsigned int pllr;
> > -	u16 mul;
> > -	u8 div;
> > -
> > -	regmap_read(pll->regmap, PLL_REG(pll->id), &pllr);
> > -
> > -	div = PLL_DIV(pllr);
> > -	mul = PLL_MUL(pllr, pll->layout);
> > -
> > -	if (!div || !mul)
> > -		return 0;
> >  
> > -	return (parent_rate / div) * (mul + 1);
> > +	return (parent_rate / pll->div) * (pll->mul + 1);
> >  }
> >  
> >  static long clk_pll_get_best_div_mul(struct clk_pll *pll, unsigned long rate,
> 