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

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Date:   Tue, 15 May 2018 23:39:42 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marcin Ziemianowicz <marcin@...mianowicz.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc:     Marcin Ziemianowicz <marcin@...mianowicz.com>,
        stable@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4] clk: at91: PLL recalc_rate() now using cached MUL and DIV
 values

Quoting Marcin Ziemianowicz (2018-04-29 12:01:11)
> 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@...r.kernel.org>
> Signed-off-by: Marcin Ziemianowicz <marcin@...mianowicz.com>
> ---

Applied to clk-next