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Ivanov" To: Michael Turquette , Stephen Boyd , Nicolas Saenz Julienne , Florian Fainelli , Ray Jui , Scott Branden , bcm-kernel-feedback-list@broadcom.com, Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: "Ivan T. Ivanov" , Phil Elwell , kernel test robot , linux-clk@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: [PATCH v2] clk: bcm2835: Round UART input clock up Date: Mon, 4 Apr 2022 15:51:13 +0300 Message-Id: <20220404125113.80239-1-iivanov@suse.de> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220404_055203_827161_09B0B4C6 X-CRM114-Status: GOOD ( 15.81 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org The UART clock is initialised to be as close to the requested frequency as possible without exceeding it. Now that there is a clock manager that returns the actual frequencies, an expected 48MHz clock is reported as 47999625. If the requested baudrate == requested clock/16, there is no headroom and the slight reduction in actual clock rate results in failure. If increasing a clock by less than 0.1% changes it from ..999.. to ..000.., round it up. This is reworked version of a downstream fix: https://github.com/raspberrypi/linux/commit/ab3f1b39537f6d3825b8873006fbe2fc5ff057b7 Cc: Phil Elwell Signed-off-by: Ivan T. Ivanov --- Changes since v1 Make bcm2835_clock_round() static to fix following warning when compiling for riscv: drivers/clk/bcm/clk-bcm2835.c:997:15: warning: no previous prototype for 'bcm2835_clock_round' [-Wmissing-prototypes] Reported-by: kernel test robot drivers/clk/bcm/clk-bcm2835.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c index 3ad20e75fd23..c29b643d1bf5 100644 --- a/drivers/clk/bcm/clk-bcm2835.c +++ b/drivers/clk/bcm/clk-bcm2835.c @@ -502,6 +502,8 @@ struct bcm2835_clock_data { bool low_jitter; u32 tcnt_mux; + + bool round_up; }; struct bcm2835_gate_data { @@ -992,12 +994,30 @@ static long bcm2835_clock_rate_from_divisor(struct bcm2835_clock *clock, return temp; } +static unsigned long bcm2835_clock_round(unsigned long clk) +{ + unsigned long scaler; + + /* + * If increasing a clock by less than 0.1% changes it + * from ..999.. to ..000.., round up. + */ + scaler = 1; + while (scaler * 100000 < clk) + scaler *= 10; + if ((clk + scaler - 1) / scaler % 1000 == 0) + clk = (clk / scaler + 1) * scaler; + + return clk; +} + static unsigned long bcm2835_clock_get_rate(struct clk_hw *hw, unsigned long parent_rate) { struct bcm2835_clock *clock = bcm2835_clock_from_hw(hw); struct bcm2835_cprman *cprman = clock->cprman; const struct bcm2835_clock_data *data = clock->data; + unsigned long rate; u32 div; if (data->int_bits == 0 && data->frac_bits == 0) @@ -1005,7 +1025,12 @@ static unsigned long bcm2835_clock_get_rate(struct clk_hw *hw, div = cprman_read(cprman, data->div_reg); - return bcm2835_clock_rate_from_divisor(clock, parent_rate, div); + rate = bcm2835_clock_rate_from_divisor(clock, parent_rate, div); + + if (data->round_up) + rate = bcm2835_clock_round(rate); + + return rate; } static void bcm2835_clock_wait_busy(struct bcm2835_clock *clock) @@ -2142,7 +2167,8 @@ static const struct bcm2835_clk_desc clk_desc_array[] = { .div_reg = CM_UARTDIV, .int_bits = 10, .frac_bits = 12, - .tcnt_mux = 28), + .tcnt_mux = 28, + .round_up = true), /* TV encoder clock. Only operating frequency is 108Mhz. */ [BCM2835_CLOCK_VEC] = REGISTER_PER_CLK(