diff options
| author | Nathan Barrett-Morrison <nathan.morrison@timesys.com> | 2022-11-28 11:41:47 -0500 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2022-11-29 18:45:32 +0000 |
| commit | f8fc65e50ad71c139a12a96e64eeba5005e491d5 (patch) | |
| tree | 0c050521c861a2170b7e6a56b9b84c779d237da7 /drivers/spi | |
| parent | 7ba63521a1e9d8ca6fb55ead19e6e2b850b8fd80 (diff) | |
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 <nathan.morrison@timesys.com>
Link: https://lore.kernel.org/r/20221128164147.158441-1-nathan.morrison@timesys.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-cadence-quadspi.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c index 4219113cf36b..676313e1bdad 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; |