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

[Alexandru Elisei <alexandru.elisei@arm.com>]

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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