On 4/22/19 3:17 AM, Li Qiang wrote: > > > Philippe Mathieu-Daudé <phi...@redhat.com <mailto:phi...@redhat.com>> 于 > 2019年4月21日周日 下午6:28写道: > > Hi Li, > > The patch title is not very descriptive, maybe "allow 64-bit access" > > > On 4/20/19 6:14 PM, Li Qiang wrote: > > The edu spec said, the MMIO area can be accessed by 8 bytes. > > or 64-bit... > > > However currently the 'max_access_size' is not so the MMIO > > access dispatch can only access 4 bytes one time. This patch > > 32-bit > > > fixes this to respect the spec. > > > > Notice: here the 'min_access_size' is not a must, I set this > > for completement. > > Which one? valid/impl? I think you can drop this comment from the commit > description. > > > Both needed. from memory_access_size, if we has no valid.max_access_size, > this function will set it to 4. > > static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr) > { > unsigned access_size_max = mr->ops->valid.max_access_size; > > /* Regions are assumed to support 1-4 byte accesses unless > otherwise specified. */ > if (access_size_max == 0) { > access_size_max = 4; > } > ... > } > > From access_with_adjusted_size, if we has no impl.max_access_size, > this function will set it to 4. > > ps: I will appreciate if anyone can explain what's the meaning of valid > and impl's min/max_access_size > and how it affects the behavior.
"valid" describes the valid access from the bus to the device. Indeed in the EDU case those are 4 and 8. "impl" describes the accesses implemented by the QEMU device model. The developper who writes the device is free to choose the accesses he will model. If valid/impl accesses don't match, the function access_with_adjusted_size() from memory.c will adjust the bus access to the device implementation. For example, if the device only implements 1 and 2 bytes accesses, with a 1-4 valid access, if the CPU executes a 32-bit access, this function will do 2x 16-bit access to the device (incrementing the address by 2) and returns a 32-bit result. Similarly, if the CPU does a 8-bit access on a 32-bit impl device, access_with_adjusted_size() will execute a single 32-bit access to the device, then mask/shift the returned value and returns a 8-bit result to the caller. > Thanks, > Li Qiang > > > > > Signed-off-by: Li Qiang <liq...@163.com <mailto:liq...@163.com>> > > --- > > hw/misc/edu.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/hw/misc/edu.c b/hw/misc/edu.c > > index 91af452c9e..65fc32b928 100644 > > --- a/hw/misc/edu.c > > +++ b/hw/misc/edu.c > > @@ -289,6 +289,15 @@ static const MemoryRegionOps edu_mmio_ops = { > > .read = edu_mmio_read, > > .write = edu_mmio_write, > > .endianness = DEVICE_NATIVE_ENDIAN, > > + .valid = { > > + .min_access_size = 4, > > Per the spec, this is correct. > > > + .max_access_size = 8, > > Correct. > > > + }, > > + .impl = { > > + .min_access_size = 4, > > OK. > > > + .max_access_size = 8, > > Correct. > > > + }, > > + > > }; > > > > /* > > > > With title/description updated: > Reviewed-by: Philippe Mathieu-Daudé <phi...@redhat.com > <mailto:phi...@redhat.com>> >