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Mon, 29 Jun 2026 13:12:53 -0700 (PDT) Date: Mon, 29 Jun 2026 16:12:50 -0400 From: Brian Masney To: Colin Foster Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org, Shubhrajyoti Datta , Michal Simek , Stephen Boyd , Michael Turquette Subject: Re: [PATCH v1 1/3] clk: clocking-wizard: fix clock difference detection Message-ID: References: <20260506200555.2558434-1-colin.foster@in-advantage.com> <20260506200555.2558434-2-colin.foster@in-advantage.com> Precedence: bulk X-Mailing-List: linux-clk@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260506200555.2558434-2-colin.foster@in-advantage.com> User-Agent: Mutt/2.3.2 (2026-04-26) Hi Colin, On Wed, May 06, 2026 at 03:05:53PM -0500, Colin Foster wrote: > The diff calculation didn't take into account rollover. As such, a > target clock frequency below the requested rate would not be considered. > > Before this change, bogus diffs would be used to determine the closest > possible clock: > > 8<-------- > clk-wizard-test: requesting 133312500 Hz on output 0 (clock NOT enabled) > *** Clock wizard - Matching for rate 133312500 parent rate 99999000 > m = 33, d = 1, o = 25, freq = 131998680, diff = 18446744073708237796 > m = 34, d = 1, o = 26, freq = 130767923, diff = 18446744073707007039 > m = 35, d = 1, o = 26, freq = 134614038, diff = 1301538 > m = 36, d = 1, o = 27, freq = 133332000, diff = 19500 > 8<-------- > > After this change: > > 8<-------- > clk-wizard-test: requesting 133312500 Hz on output 0 (clock NOT enabled) > *** Clock wizard - Matching for rate 133312500 parent rate 99999000 > m = 33, d = 1, o = 25, freq = 131998680, diff = 1313820 > m = 35, d = 1, o = 26, freq = 134614038, diff = 1301538 > m = 36, d = 1, o = 27, freq = 133332000, diff = 19500 > 8<-------- > > Signed-off-by: Colin Foster > --- > drivers/clk/xilinx/clk-xlnx-clock-wizard.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/clk/xilinx/clk-xlnx-clock-wizard.c b/drivers/clk/xilinx/clk-xlnx-clock-wizard.c > index 032a688840d8..88b47b8cc387 100644 > --- a/drivers/clk/xilinx/clk-xlnx-clock-wizard.c > +++ b/drivers/clk/xilinx/clk-xlnx-clock-wizard.c > @@ -408,7 +408,7 @@ static int clk_wzrd_get_divisors(struct clk_hw *hw, unsigned long rate, > if (o < omin || o > omax) > continue; > freq = DIV_ROUND_CLOSEST_ULL(vco_freq, o); > - diff = freq - rate; > + diff = abs(freq - rate); > > if (diff < best_diff) { > printk("m = %d, d = %d, o = %d, freq = %llu, diff = %llu", m, d, o, freq, diff); Stephen didn't pick this up last development cycle and I'm assembling a pull for him. This doesn't apply to upstream. Please post a new version that applies cleanly. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/xilinx/clk-xlnx-clock-wizard.c#n341 Brian