The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 571426631acf46e2999c7ecd1e9d048172969a43 Mon Sep 17 00:00:00 2001 From: Billy Tsai billy_tsai@aspeedtech.com Date: Mon, 21 Feb 2022 09:27:05 +0800 Subject: [PATCH] iio: adc: aspeed: Add divider flag to fix incorrect voltage reading.

The formula for the ADC sampling period in ast2400/ast2500 is: ADC clock period = PCLK * 2 * (ADC0C[31:17] + 1) * (ADC0C[9:0]) When ADC0C[9:0] is set to 0 the sampling voltage will be lower than expected, because the hardware may not have enough time to charge/discharge to a stable voltage. This patch use the flag CLK_DIVIDER_ONE_BASED which will use the raw value read from the register, with the value of zero considered invalid to conform to the corrected formula.

Fixes: 573803234e72 ("iio: Aspeed ADC") Reported-by: Konstantin Klubnichkin kitsok@yandex-team.ru Signed-off-by: Billy Tsai billy_tsai@aspeedtech.com Reviewed-by: Joel Stanley joel@jms.id.au Link: https://lore.kernel.org/r/20220221012705.22008-1-billy_tsai@aspeedtech.com Cc: Stable@vger.kernel.org Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com

diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c index e939b84cbb56..0793d2474cdc 100644 --- a/drivers/iio/adc/aspeed_adc.c +++ b/drivers/iio/adc/aspeed_adc.c @@ -539,7 +539,9 @@ static int aspeed_adc_probe(struct platform_device *pdev) data->clk_scaler = devm_clk_hw_register_divider( &pdev->dev, clk_name, clk_parent_name, scaler_flags, data->base + ASPEED_REG_CLOCK_CONTROL, 0, - data->model_data->scaler_bit_width, 0, &data->clk_lock); + data->model_data->scaler_bit_width, + data->model_data->need_prescaler ? CLK_DIVIDER_ONE_BASED : 0, + &data->clk_lock); if (IS_ERR(data->clk_scaler)) return PTR_ERR(data->clk_scaler);