| Message ID | alpine.DEB.2.21.2106260524430.37803@angie.orcam.me.uk |
|---|---|
| State | New |
| Headers | show |
| Series | serial, Malta: Fixes to make the CBUS UART work big-endian | expand |
On Sat, Jun 26, 2021 at 6:11 AM Maciej W. Rozycki <macro@orcam.me.uk> wrote: > > Correct big-endian accesses to the CBUS UART, a Malta on-board discrete > TI16C550C part wired directly to the system controller's device bus, and > do not use byte swapping with the 32-bit accesses to the device. > > The CBUS is used for devices such as the boot flash memory needed early > on in system bootstrap even before PCI has been initialised. Therefore > it uses the system controller's device bus, which follows the endianness > set with the CPU, which means no byte-swapping is ever required for data > accesses to CBUS, unlike with PCI. > > The CBUS UART uses the UPIO_MEM32 access method, that is the `readl' and > `writel' MMIO accessors, which on the MIPS platform imply byte-swapping > with PCI systems. Consequently the wrong byte lane is accessed with the > big-endian configuration and the UART is not correctly accessed. > > As it happens the UPIO_MEM32BE access method makes use of the `ioread32' > and `iowrite32' MMIO accessors, which still use `readl' and `writel' > respectively, however they byte-swap data passed, effectively cancelling > swapping done with the accessors themselves and making it suitable for > the CBUS UART. > > Make the CBUS UART switch between UPIO_MEM32 and UPIO_MEM32BE then, > based on the endianness selected. With this change in place the device > is correctly recognised with big-endian Malta at boot, along with the > Super I/O devices behind PCI: > > Serial: 8250/16550 driver, 5 ports, IRQ sharing enabled > printk: console [ttyS0] disabled > serial8250.0: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A > printk: console [ttyS0] enabled > printk: bootconsole [uart8250] disabled > serial8250.0: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A > serial8250.0: ttyS2 at MMIO 0x1f000900 (irq = 20, base_baud = 230400) is a 16550A > > Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> > Fixes: e7c4782f92fc ("[MIPS] Put an end to <asm/serial.h>'s long and annyoing existence") > Cc: stable@vger.kernel.org # v2.6.23+ > --- > Changes from v1: > > - Remove console message duplicates from the commit description. > --- > arch/mips/mti-malta/malta-platform.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Index: linux-macro-ide-tty/arch/mips/mti-malta/malta-platform.c =================================================================== --- linux-macro-ide-tty.orig/arch/mips/mti-malta/malta-platform.c +++ linux-macro-ide-tty/arch/mips/mti-malta/malta-platform.c @@ -48,7 +48,8 @@ static struct plat_serial8250_port uart8 .mapbase = 0x1f000900, /* The CBUS UART */ .irq = MIPS_CPU_IRQ_BASE + MIPSCPU_INT_MB2, .uartclk = 3686400, /* Twice the usual clk! */ - .iotype = UPIO_MEM32, + .iotype = IS_ENABLED(CONFIG_CPU_BIG_ENDIAN) ? + UPIO_MEM32BE : UPIO_MEM32, .flags = CBUS_UART_FLAGS, .regshift = 3, },
Correct big-endian accesses to the CBUS UART, a Malta on-board discrete TI16C550C part wired directly to the system controller's device bus, and do not use byte swapping with the 32-bit accesses to the device. The CBUS is used for devices such as the boot flash memory needed early on in system bootstrap even before PCI has been initialised. Therefore it uses the system controller's device bus, which follows the endianness set with the CPU, which means no byte-swapping is ever required for data accesses to CBUS, unlike with PCI. The CBUS UART uses the UPIO_MEM32 access method, that is the `readl' and `writel' MMIO accessors, which on the MIPS platform imply byte-swapping with PCI systems. Consequently the wrong byte lane is accessed with the big-endian configuration and the UART is not correctly accessed. As it happens the UPIO_MEM32BE access method makes use of the `ioread32' and `iowrite32' MMIO accessors, which still use `readl' and `writel' respectively, however they byte-swap data passed, effectively cancelling swapping done with the accessors themselves and making it suitable for the CBUS UART. Make the CBUS UART switch between UPIO_MEM32 and UPIO_MEM32BE then, based on the endianness selected. With this change in place the device is correctly recognised with big-endian Malta at boot, along with the Super I/O devices behind PCI: Serial: 8250/16550 driver, 5 ports, IRQ sharing enabled printk: console [ttyS0] disabled serial8250.0: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A printk: console [ttyS0] enabled printk: bootconsole [uart8250] disabled serial8250.0: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A serial8250.0: ttyS2 at MMIO 0x1f000900 (irq = 20, base_baud = 230400) is a 16550A Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Fixes: e7c4782f92fc ("[MIPS] Put an end to <asm/serial.h>'s long and annyoing existence") Cc: stable@vger.kernel.org # v2.6.23+ --- Changes from v1: - Remove console message duplicates from the commit description. --- arch/mips/mti-malta/malta-platform.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) linux-mips-malta-cbus-uart-be.diff