Philippe Mathieu-Daudé <f4...@amsat.org> writes: > On 6/25/20 10:12 AM, Philippe Mathieu-Daudé wrote: >> On 6/25/20 8:37 AM, Markus Armbruster wrote: >>> Cédric Le Goater <c...@kaod.org> writes: >>> >>>> On 6/22/20 10:31 AM, Philippe Mathieu-Daudé wrote: >>>>> On 6/22/20 8:27 AM, Cédric Le Goater wrote: >>>>>> On 6/21/20 12:58 AM, Philippe Mathieu-Daudé wrote: >>>>>>> Add a description field to distinguish between multiple devices. >>> >>> Pardon my lack of imagination: how does this help you with debugging? >> >> Ah, the patch subject is indeed incorrect, this should be: >> "... for *tracing* purpose" (I use tracing when debugging). >> >> In the next patch, we use the 'description' property: >> >> +# pca9552.c >> +pca9552_gpio_status(const char *description, const char *buf) "%s GPIOs >> 0-15 [%s]" >> >> So when the machine has multiple PCA9552 and guest accesses both, >> we can distinct which one is used. For me having "pca1" / "pca0" >> is easier to follow than the address of the QOM object. >> >>> >>>>>> Reviewed-by: Cédric Le Goater <c...@kaod.org> >>>>>> >>>>>> Could it be a QOM attribute ? >>>>> >>>>> What do you call a 'QOM attribute'? >>>>> Is it what qdev properties implement? >>>>> (in this case via DEFINE_PROP_STRING). >>>> >>>> I meant a default Object property, which would apply to all Objects. >>> >>> Good point. Many devices have multiple component objects of the same >>> type. >>> >>>> What you did is fine, so : >>>> >>>> Reviewed-by: Cédric Le Goater <c...@kaod.org> >>>> >>>> but, may be, a well defined child name is enough for the purpose. >>> >>> object_get_canonical_path() returns a distinct path for each (component) >>> object. The path components are the child property names. >>> >>> Properties can have descriptions: object_property_set_description(). >> >> TIL object_property_set_description :> >> >> Ah, there is no equivalent object_property_get_description(), >> we have to use object_get_canonical_path(). Hmm, not obvious. >> >>> >>> Sufficient? >> >> I don't know... This seems a complex way to do something simple... >> This is already a QDEV. Having to use QOM API seems going >> backward, since we have the DEFINE_PROP_STRING() macros available >> in "hw/qdev-properties.h". >> >> Maybe I'm not seeing the advantages clearly. I'll try later. > > The canonical path is not very helpful in trace log...
Why? Okay, I checked the code. Since the devices in question don't get a composition tree parent assigned, realize puts them in the /machine/unattached orphanage. The canonical path is something like "/machine/unattached/device[6]", which is less than clear. The components of the canonical path are the names of the QOM child properties. object_get_canonical_path_component() returns the last one, in this case "device[6]". If we made the devices QOM children of some other device, we could name the child properties "pca0" and "pca1". object_get_canonical_path_component() would then return the strings you want to see. We make a device a QOM child of some QOM parent device only if the child is a component device of the parent (hence the name "composition tree"). Are these devices integral components of something else, or are they separate chips? > The description I set matches the hardware definitions > and is easier to follow, see patch #6 (where it is set) > where the description comes from: > > https://www.mail-archive.com/qemu-devel@nongnu.org/msg714658.html > > Description name taken from: > https://github.com/open-power/witherspoon-xml/blob/master/witherspoon.xml > > So in this particular case I don't find the canonical pathname > practical (from an hardware debugging perspective). Personally, I'd be content with i2c bus and address for debugging purposes. The i2c buses *are* components: canonical paths look like "/machine/soc/i2c/aspeed.i2c.3". The combination of object_get_canonical_path_component(dev) and object_property_get_uint(dev, "address", &error_abort) identifies any i2c device on this machine, not just the two you decorate with a description string.
