Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2 2/4] driver core: handle -EPROBE_DEFER from bus_type.match() | From | Marek Szyprowski <> | Date | Tue, 01 Dec 2015 10:25:46 +0100 |
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Hello,
On 2015-11-30 14:36, Ulf Hansson wrote: > On 26 November 2015 at 13:49, Marek Szyprowski <m.szyprowski@samsung.com> wrote: >> From: Tomeu Vizoso <tomeu.vizoso@collabora.com> >> >> Lets implementations of the match() callback in struct bus_type to > /s/Lets/Allow > >> return errors and if it's -EPROBE_DEFER then queue the device for >> deferred probing. >> >> This is useful to buses such as AMBA in which devices are registered >> before their matching information can be retrieved from the HW >> (typically because a clock driver hasn't probed yet). >> >> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com> >> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> >> --- >> drivers/base/dd.c | 24 ++++++++++++++++++++++-- >> include/linux/device.h | 2 +- >> 2 files changed, 23 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/base/dd.c b/drivers/base/dd.c >> index a641cf3..a20c119 100644 >> --- a/drivers/base/dd.c >> +++ b/drivers/base/dd.c >> @@ -490,6 +490,7 @@ static int __device_attach_driver(struct device_driver *drv, void *_data) >> struct device_attach_data *data = _data; >> struct device *dev = data->dev; >> bool async_allowed; >> + int ret; >> >> /* >> * Check if device has already been claimed. This may >> @@ -500,8 +501,17 @@ static int __device_attach_driver(struct device_driver *drv, void *_data) >> if (dev->driver) >> return -EBUSY; >> >> - if (!driver_match_device(drv, dev)) >> + ret = driver_match_device(drv, dev); >> + if (!ret) >> return 0; >> + else if (ret < 0) { > Depending on what happens with the added dev_warn() below, perhaps a > switch statement can make it a bit clearer, instead of these messy if > clauses?
Frankly, I have no idea how to convert this to switch statement and make the code easier to read. Please note that we have the following 4 cases:
ret > 0: positive match ret == 0: negative match ret == -EPROBE_DEFER: deferred probe ret < 0: other, unknown error
Another way to encode this logic is the following code:
if (ret == 0) { /* no match */ return 0; } else if (ret == -EPROBE_DEFER) { dev_dbg(dev, "Device match requests probe deferral\n"); driver_deferred_probe_add(dev); return ret; } else if (ret < 0) { dev_dbg(dev, "Bus failed to match device: %d", ret); return ret; } /* ret > 0 means positive match */
>> + if (ret == -EPROBE_DEFER) { >> + dev_dbg(dev, "Device match requests probe deferral\n"); >> + driver_deferred_probe_add(dev); >> + } else >> + dev_warn(dev, "Bus failed to match device: %d", ret); > Greg commented on this before, as it may introduce some noise [1]. > > I started browsing various bus’s implementation of the ->match() > callback. A quick search tells me that most implementations are > following the Documentation/driver-model/porting.txt, which means > returning 0 or 1. Actually I couldn't find anyone returning any other > value, though it was a quick search. > > On the other hand, include/linux/device.h states a "non-zero" value is > allowed to be return, so there's a tiny conflict between the code and > the documentation. I guess we should fix that!?
Okay, I will update the documentation as well.
> No matter what, I realize that it could be useful to print a message > when receiving a negative error code, maybe dev_dbg() could be > sufficient? > >> + return ret; >> + } >> >> async_allowed = driver_allows_async_probing(drv); >> >> @@ -621,6 +631,7 @@ void device_initial_probe(struct device *dev) >> static int __driver_attach(struct device *dev, void *data) >> { >> struct device_driver *drv = data; >> + int ret; >> >> /* >> * Lock device and try to bind to it. We drop the error >> @@ -632,8 +643,17 @@ static int __driver_attach(struct device *dev, void *data) >> * is an error. >> */ >> >> - if (!driver_match_device(drv, dev)) >> + ret = driver_match_device(drv, dev); >> + if (!ret) >> + return 0; >> + else if (ret < 0) { >> + if (ret == -EPROBE_DEFER) { >> + dev_dbg(dev, "Device match requests probe deferral\n"); >> + driver_deferred_probe_add(dev); >> + } else >> + dev_warn(dev, "Bus failed to match device: %d", ret); >> return 0; >> + } >> >> if (dev->parent) /* Needed for USB */ >> device_lock(dev->parent); >> diff --git a/include/linux/device.h b/include/linux/device.h >> index b8f411b..d4e7d1f 100644 >> --- a/include/linux/device.h >> +++ b/include/linux/device.h >> @@ -70,7 +70,7 @@ extern void bus_remove_file(struct bus_type *, struct bus_attribute *); >> * @dev_groups: Default attributes of the devices on the bus. >> * @drv_groups: Default attributes of the device drivers on the bus. >> * @match: Called, perhaps multiple times, whenever a new device or driver >> - * is added for this bus. It should return a nonzero value if the >> + * is added for this bus. It should return a positive value if the >> * given device can be handled by the given driver. >> * @uevent: Called when a device is added, removed, or a few other things >> * that generate uevents to add the environment variables. >> -- >> 1.9.2
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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