diff options
Diffstat (limited to 'drivers/serial')
| -rw-r--r-- | drivers/serial/serial_mvebu_a3700.c | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/drivers/serial/serial_mvebu_a3700.c b/drivers/serial/serial_mvebu_a3700.c index ba2ac5917f..c7e66fef87 100644 --- a/drivers/serial/serial_mvebu_a3700.c +++ b/drivers/serial/serial_mvebu_a3700.c @@ -204,6 +204,71 @@ static int mvebu_serial_probe(struct udevice *dev) return 0; } +static int mvebu_serial_remove(struct udevice *dev) +{ + struct mvebu_plat *plat = dev_get_plat(dev); + void __iomem *base = plat->base; + ulong new_parent_rate, parent_rate; + u32 new_divider, divider; + u32 new_oversampling; + u32 oversampling; + u32 d1, d2; + + /* + * Switch UART base clock back to XTAL because older Linux kernel + * expects it. Otherwise it does not calculate UART divisor correctly + * and therefore UART does not work in kernel. + */ + divider = readl(base + UART_BAUD_REG); + if (!(divider & BIT(19))) /* UART already uses XTAL */ + return 0; + + /* Read current divisors settings */ + d1 = (divider >> 15) & 7; + d2 = (divider >> 12) & 7; + parent_rate = plat->tbg_rate; + divider &= 1023; + oversampling = readl(base + UART_POSSR_REG) & 63; + if (!oversampling) + oversampling = 16; + + /* Calculate new divisor against XTAL clock without changing baudrate */ + new_oversampling = 0; + new_parent_rate = get_ref_clk() * 1000000; + new_divider = DIV_ROUND_CLOSEST(new_parent_rate * divider * d1 * d2 * + oversampling, parent_rate * 16); + + /* + * UART does not work reliably when XTAL divisor is smaller than 4. + * In this case we do not switch UART parent to XTAL. User either + * configured unsupported settings or has newer kernel with patches + * which allow usage of non-XTAL clock as a parent clock. + */ + if (new_divider < 4) + return 0; + + /* + * If new divisor is larger than maximal supported, try to switch + * from default x16 scheme to oversampling with maximal factor 63. + */ + if (new_divider > 1023) { + new_oversampling = 63; + new_divider = DIV_ROUND_CLOSEST(new_parent_rate * divider * d1 * + d2 * oversampling, + parent_rate * new_oversampling); + if (new_divider < 4 || new_divider > 1023) + return 0; + } + + while (!(readl(base + UART_STATUS_REG) & UART_STATUS_TX_EMPTY)) + ; + + writel(new_divider, base + UART_BAUD_REG); + writel(new_oversampling, base + UART_POSSR_REG); + + return 0; +} + static int mvebu_serial_of_to_plat(struct udevice *dev) { struct mvebu_plat *plat = dev_get_plat(dev); @@ -232,6 +297,8 @@ U_BOOT_DRIVER(serial_mvebu) = { .of_to_plat = mvebu_serial_of_to_plat, .plat_auto = sizeof(struct mvebu_plat), .probe = mvebu_serial_probe, + .remove = mvebu_serial_remove, + .flags = DM_FLAG_OS_PREPARE, .ops = &mvebu_serial_ops, }; |