From: Remi Pommarel <repk@triplefau.lt>
To: Eric Anholt <eric@anholt.net>
Cc: Stephen Warren <swarren@wwwdotorg.org>,
Lee Jones <lee@kernel.org>,
Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@codeaurora.org>,
linux-rpi-kernel@lists.infradead.org, linux-clk@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/3] clk: bcm2835: Support for clock parent selection
Date: Wed, 18 Nov 2015 20:24:23 +0100 [thread overview]
Message-ID: <20151118192423.GC491@cruxbox> (raw)
In-Reply-To: <87egfn2m9y.fsf@eliezer.anholt.net>
On Wed, Nov 18, 2015 at 10:30:17AM -0800, Eric Anholt wrote:
[...]
> > +static int bcm2835_clock_determine_rate(struct clk_hw *hw,
> > + struct clk_rate_request *req)
> > +{
> > + struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw);
> > + struct clk_hw *parent, *best_parent = NULL;
> > + struct clk_rate_request parent_req;
> > + unsigned long rate, best_rate = 0;
> > + unsigned long prate, best_prate = 0;
> > + size_t i;
> > + u32 div;
> > +
> > + /*
> > + * Select parent clock that results in the closest but lower rate
> > + */
> > + for (i = 0; i < clk_hw_get_num_parents(hw); ++i) {
> > + parent = clk_hw_get_parent_by_index(hw, i);
> > + if (!parent)
> > + continue;
> > + parent_req = *req;
>
> parent_req appears dead, so it should be removed.
Yes, will do thanks.
> > + prate = clk_hw_get_rate(parent);
> > + div = bcm2835_clock_choose_div(hw, req->rate, prate);
> > + rate = bcm2835_clock_rate_from_divisor(clock, prate, div);
> > + if (rate > best_rate && rate <= req->rate) {
> > + best_parent = parent;
> > + best_prate = prate;
> > + best_rate = rate;
> > + }
> > + }
> > +
> > + if (!best_parent)
> > + return -EINVAL;
> > +
> > + req->best_parent_hw = best_parent;
> > + req->best_parent_rate = best_prate;
>
> I think you're supposed to req->rate = best_rate, here, too. With these
> two fixes,
I did not set req->rate to best_rate in order to avoid rounding down
twice the actual clock rate.
Indeed with patch 1 from this patchset bcm2835_clock_choose_div()
chooses a divisor that produces a rate lower or equal to the requested
one. As we call bcm2835_clock_choose_div() twice when using
clk_set_rate() (once with ->determine_rate() and once with ->set_rate()),
if I set req->rate in bcm2835_clock_determine_rate to the rounded down
one, the final rate will likely be again rounded down in
bcm2835_clock_set_rate().
Thanks,
--
Rémi Pommarel
next prev parent reply other threads:[~2015-11-18 19:24 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-11 14:22 [PATCH v2 0/3] Add PWM clock support for bcm2835 Remi Pommarel
2015-11-11 14:22 ` [PATCH v2 1/3] clk: bcm2835: Always round up clock divisor Remi Pommarel
2015-11-18 18:25 ` Eric Anholt
2015-11-18 19:11 ` Remi Pommarel
2015-12-02 22:21 ` Remi Pommarel
2015-12-04 0:31 ` Eric Anholt
2015-11-11 14:22 ` [PATCH v2 2/3] clk: bcm2835: Support for clock parent selection Remi Pommarel
2015-11-18 18:30 ` Eric Anholt
2015-11-18 19:24 ` Remi Pommarel [this message]
2015-12-04 0:37 ` Eric Anholt
2015-12-04 20:37 ` Remi Pommarel
2015-12-06 0:19 ` Eric Anholt
2015-11-11 14:22 ` [PATCH v2 3/3] clk: bcm2835: Add PWM clock support Remi Pommarel
2015-11-18 18:32 ` Eric Anholt
2015-11-18 19:26 ` Remi Pommarel
2015-11-28 20:52 ` [PATCH v2 0/3] Add PWM clock support for bcm2835 Stefan Wahren
2015-11-29 0:31 ` Remi Pommarel
2015-11-29 21:22 ` Stefan Wahren
2015-11-29 22:25 ` Remi Pommarel
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