Re: [PATCH kvmtool 20/21] hw/serial: ARM/arm64: Use MMIO at higher addresses

Alexandru Elisei
2021-02-18T12:37:34Z

Hi Andre,

On 2/17/21 4:48 PM, Alexandru Elisei wrote:
> Hi Andre,
>
> On 12/10/20 2:29 PM, Andre Przywara wrote:
>> Using the UART devices at their legacy I/O addresses as set by IBM in
>> 1981 was a kludge we used for simplicity on ARM platforms as well.
>> However this imposes problems due to their missing alignment and overlap
>> with the PCI I/O address space.
>>
>> Now that we can switch a device easily between using ioports and MMIO,
>> let's move the UARTs out of the first 4K of memory on ARM platforms.
>>
>> That should be transparent for well behaved guests, since the change is
>> naturally reflected in the device tree. Even "earlycon" keeps working,
>> as the stdout-path property is adjusted automatically.
>>
>> People providing direct earlycon parameters via the command line need to
>> adjust it to: "earlycon=uart,mmio,0x1000000".
>>
>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>> ---
>> hw/serial.c | 52 ++++++++++++++++++++++++++++++++++++----------------
>> 1 file changed, 36 insertions(+), 16 deletions(-)
>>
>> diff --git a/hw/serial.c b/hw/serial.c
>> index d840eebc..00fb3aa8 100644
>> --- a/hw/serial.c
>> +++ b/hw/serial.c
>> @@ -13,6 +13,24 @@
>>
>> #include <pthread.h>
>>
>> +#if defined(CONFIG_ARM) || defined(CONFIG_ARM64)
>> +#define serial_iobase(nr) (0x1000000 + (nr) * 0x1000)
>> +#define serial_irq(nr) (32 + (nr))
>> +#define SERIAL8250_BUS_TYPE DEVICE_BUS_MMIO
>> +#else
>> +#define serial_iobase_0 0x3f8
>> +#define serial_iobase_1 0x2f8
>> +#define serial_iobase_2 0x3e8
>> +#define serial_iobase_3 0x2e8
>> +#define serial_irq_0 4
>> +#define serial_irq_1 3
>> +#define serial_irq_2 4
>> +#define serial_irq_3 3
> Nitpick: serial_iobase_* and serial_irq_* could be changed to have two leading
> underscores, to stress the fact that they are helpers for serial_iobase() and
> serial_irq() and are not meant to be used by themselves. But that's just personal
> preference, otherwise the patch looks really nice and clean:
>
> Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>

I gave it more thought and I think I spoke too soon. I think it would be good to
document in the commit message how you came to the base MMIO address and size
(even if it was just a nice looking number). Also, the CFI flash device has its
memory range described in the memory layout for the architecture, in
arm/include/arm-common/kvm-arch.h. I think it would be a good idea to put the
serial region there, to prevent regressions in the future.

I did the math to make sure there's no overlap with the ioport region (16M >> 16K)
or the flash region (16M + 0x4000 < 32M). I also tested the changes with a kernel
with 4K and 64K pages (I can't access any hardware with 16K pages at the moment),
and everything worked as expected.

Thanks,

Alex

> Thanks,
>
> Alex
>
>> +#define serial_iobase(nr) serial_iobase_##nr
>> +#define serial_irq(nr) serial_irq_##nr
>> +#define SERIAL8250_BUS_TYPE DEVICE_BUS_IOPORT
>> +#endif
>> +
>> /*
>> * This fakes a U6_16550A. The fifo len needs to be 64 as the kernel
>> * expects that for autodetection.
>> @@ -27,7 +45,7 @@ struct serial8250_device {
>> struct mutex mutex;
>> u8 id;
>>
>> - u16 iobase;
>> + u32 iobase;
>> u8 irq;
>> u8 irq_state;
>> int txcnt;
>> @@ -65,56 +83,56 @@ static struct serial8250_device devices[] = {
>> /* ttyS0 */
>> [0] = {
>> .dev_hdr = {
>> - .bus_type = DEVICE_BUS_IOPORT,
>> + .bus_type = SERIAL8250_BUS_TYPE,
>> .data = serial8250_generate_fdt_node,
>> },
>> .mutex = MUTEX_INITIALIZER,
>>
>> .id = 0,
>> - .iobase = 0x3f8,
>> - .irq = 4,
>> + .iobase = serial_iobase(0),
>> + .irq = serial_irq(0),
>>
>> SERIAL_REGS_SETTING
>> },
>> /* ttyS1 */
>> [1] = {
>> .dev_hdr = {
>> - .bus_type = DEVICE_BUS_IOPORT,
>> + .bus_type = SERIAL8250_BUS_TYPE,
>> .data = serial8250_generate_fdt_node,
>> },
>> .mutex = MUTEX_INITIALIZER,
>>
>> .id = 1,
>> - .iobase = 0x2f8,
>> - .irq = 3,
>> + .iobase = serial_iobase(1),
>> + .irq = serial_irq(1),
>>
>> SERIAL_REGS_SETTING
>> },
>> /* ttyS2 */
>> [2] = {
>> .dev_hdr = {
>> - .bus_type = DEVICE_BUS_IOPORT,
>> + .bus_type = SERIAL8250_BUS_TYPE,
>> .data = serial8250_generate_fdt_node,
>> },
>> .mutex = MUTEX_INITIALIZER,
>>
>> .id = 2,
>> - .iobase = 0x3e8,
>> - .irq = 4,
>> + .iobase = serial_iobase(2),
>> + .irq = serial_irq(2),
>>
>> SERIAL_REGS_SETTING
>> },
>> /* ttyS3 */
>> [3] = {
>> .dev_hdr = {
>> - .bus_type = DEVICE_BUS_IOPORT,
>> + .bus_type = SERIAL8250_BUS_TYPE,
>> .data = serial8250_generate_fdt_node,
>> },
>> .mutex = MUTEX_INITIALIZER,
>>
>> .id = 3,
>> - .iobase = 0x2e8,
>> - .irq = 3,
>> + .iobase = serial_iobase(3),
>> + .irq = serial_irq(3),
>>
>> SERIAL_REGS_SETTING
>> },
>> @@ -444,7 +462,8 @@ static int serial8250__device_init(struct kvm *kvm,
>> return r;
>>
>> ioport__map_irq(&dev->irq);
>> - r = kvm__register_pio(kvm, dev->iobase, 8, serial8250_mmio, dev);
>> + r = kvm__register_iotrap(kvm, dev->iobase, 8, serial8250_mmio, dev,
>> + SERIAL8250_BUS_TYPE);
>>
>> return r;
>> }
>> @@ -467,7 +486,7 @@ cleanup:
>> for (j = 0; j <= i; j++) {
>> struct serial8250_device *dev = &devices[j];
>>
>> - kvm__deregister_pio(kvm, dev->iobase);
>> + kvm__deregister_iotrap(kvm, dev->iobase, SERIAL8250_BUS_TYPE);
>> device__unregister(&dev->dev_hdr);
>> }
>>
>> @@ -483,7 +502,8 @@ int serial8250__exit(struct kvm *kvm)
>> for (i = 0; i < ARRAY_SIZE(devices); i++) {
>> struct serial8250_device *dev = &devices[i];
>>
>> - r = kvm__deregister_pio(kvm, dev->iobase);
>> + r = kvm__deregister_iotrap(kvm, dev->iobase,
>> + SERIAL8250_BUS_TYPE);
>> if (r < 0)
>> return r;
>> device__unregister(&dev->dev_hdr);
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