From: Nathan Barrett-Morrison Date: Mon, 28 Nov 2022 16:41:47 +0000 (-0500) Subject: spi: cadence-quadspi: Add minimum operable clock rate warning to baudrate divisor... X-Git-Tag: v6.6.17~5835^2~8 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f8fc65e50ad71c139a12a96e64eeba5005e491d5;p=platform%2Fkernel%2Flinux-rpi.git spi: cadence-quadspi: Add minimum operable clock rate warning to baudrate divisor calculation This Cadence QSPI IP has a 4-bit clock divisor field for baud rate division. For example: 0b0000 = /2 0b0001 = /4 0b0010 = /6 ... 0b1111 = /32 The maximum divisor is 32 (when div = CQSPI_REG_CONFIG_BAUD_MASK). If we assume a reference clock of 500MHz and we set our spi-max-frequency to something low, such as 10 MHz. The calculated bit field for the divisor ends up being: DIV_ROUND_UP(500000000/(2*10000000))-1 = 25 25 is 0b11001... which truncates to a divisor field of 0b1001 (or /20). This is higher than our anticipated max-frequency of 10MHz (500MHz/20 = 25 MHz). Instead, let's make sure we're always using the maximum divisor (/32) in this case and give the user a warning about the rate adjustment. Signed-off-by: Nathan Barrett-Morrison Link: https://lore.kernel.org/r/20221128164147.158441-1-nathan.morrison@timesys.com Signed-off-by: Mark Brown --- diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c index 4219113..676313e 100644 --- a/drivers/spi/spi-cadence-quadspi.c +++ b/drivers/spi/spi-cadence-quadspi.c @@ -1119,6 +1119,14 @@ static void cqspi_config_baudrate_div(struct cqspi_st *cqspi) /* Recalculate the baudrate divisor based on QSPI specification. */ div = DIV_ROUND_UP(ref_clk_hz, 2 * cqspi->sclk) - 1; + /* Maximum baud divisor */ + if (div > CQSPI_REG_CONFIG_BAUD_MASK) { + div = CQSPI_REG_CONFIG_BAUD_MASK; + dev_warn(&cqspi->pdev->dev, + "Unable to adjust clock <= %d hz. Reduced to %d hz\n", + cqspi->sclk, ref_clk_hz/((div+1)*2)); + } + reg = readl(reg_base + CQSPI_REG_CONFIG); reg &= ~(CQSPI_REG_CONFIG_BAUD_MASK << CQSPI_REG_CONFIG_BAUD_LSB); reg |= (div & CQSPI_REG_CONFIG_BAUD_MASK) << CQSPI_REG_CONFIG_BAUD_LSB;