Messages in this thread | | | Date | Thu, 26 Sep 2019 07:33:21 -0700 | From | mnalajal@codeauro ... | Subject | Re: [PATCH] base: soc: Export soc_device_to_device API |
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On 2019-09-23 21:50, Greg KH wrote: > On Mon, Sep 23, 2019 at 02:35:33PM -0700, mnalajal@codeaurora.org > wrote: >> On 2019-09-19 23:10, Greg KH wrote: >> > On Thu, Sep 19, 2019 at 08:36:51PM -0700, Bjorn Andersson wrote: >> > > On Thu 19 Sep 15:45 PDT 2019, Greg KH wrote: >> > > >> > > > On Thu, Sep 19, 2019 at 03:40:17PM -0700, Bjorn Andersson wrote: >> > > > > On Thu 19 Sep 15:25 PDT 2019, Greg KH wrote: >> > > > > >> > > > > > On Thu, Sep 19, 2019 at 03:14:56PM -0700, Bjorn Andersson wrote: >> > > > > > > On Thu 19 Sep 14:58 PDT 2019, Greg KH wrote: >> > > > > > > >> > > > > > > > On Thu, Sep 19, 2019 at 02:53:00PM -0700, Bjorn Andersson wrote: >> > > > > > > > > On Thu 19 Sep 14:32 PDT 2019, Greg KH wrote: >> > > > > > > > > >> > > > > > > > > > On Thu, Sep 19, 2019 at 02:13:44PM -0700, Murali Nalajala wrote: >> > > > > > > > > > > If the soc drivers want to add custom sysfs entries it needs to >> > > > > > > > > > > access "dev" field in "struct soc_device". This can be achieved >> > > > > > > > > > > by "soc_device_to_device" API. Soc drivers which are built as a >> > > > > > > > > > > module they need above API to be exported. Otherwise one can >> > > > > > > > > > > observe compilation issues. >> > > > > > > > > > > >> > > > > > > > > > > Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org> >> > > > > > > > > > > --- >> > > > > > > > > > > drivers/base/soc.c | 1 + >> > > > > > > > > > > 1 file changed, 1 insertion(+) >> > > > > > > > > > > >> > > > > > > > > > > diff --git a/drivers/base/soc.c b/drivers/base/soc.c >> > > > > > > > > > > index 7c0c5ca..4ad52f6 100644 >> > > > > > > > > > > --- a/drivers/base/soc.c >> > > > > > > > > > > +++ b/drivers/base/soc.c >> > > > > > > > > > > @@ -41,6 +41,7 @@ struct device *soc_device_to_device(struct soc_device *soc_dev) >> > > > > > > > > > > { >> > > > > > > > > > > return &soc_dev->dev; >> > > > > > > > > > > } >> > > > > > > > > > > +EXPORT_SYMBOL_GPL(soc_device_to_device); >> > > > > > > > > > > >> > > > > > > > > > > static umode_t soc_attribute_mode(struct kobject *kobj, >> > > > > > > > > > > struct attribute *attr, >> > > > > > > > > > >> > > > > > > > > > What in-kernel driver needs this? >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > > Half of the drivers interacting with the soc driver calls this API, >> > > > > > > > > several of these I see no reason for being builtin (e.g. >> > > > > > > > > ux500 andversatile). So I think this patch makes sense to allow us to >> > > > > > > > > build these as modules. >> > > > > > > > > >> > > > > > > > > > Is linux-next breaking without this? >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > > No, we postponed the addition of any sysfs attributes in the Qualcomm >> > > > > > > > > socinfo driver. >> > > > > > > > > >> > > > > > > > > > We don't export things unless we have a user of the export. >> > > > > > > > > > >> > > > > > > > > > Also, adding "custom" sysfs attributes is almost always not the correct >> > > > > > > > > > thing to do at all. The driver should be doing it, by setting up the >> > > > > > > > > > attribute group properly so that the driver core can do it automatically >> > > > > > > > > > for it. >> > > > > > > > > > >> > > > > > > > > > No driver should be doing individual add/remove of sysfs files. If it >> > > > > > > > > > does so, it is almost guaranteed to be doing it incorrectly and racing >> > > > > > > > > > userspace. >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > > The problem here is that the attributes are expected to be attached to >> > > > > > > > > the soc driver, which is separate from the platform-specific drivers. So >> > > > > > > > > there's no way to do platform specific attributes the right way. >> > > > > > > > > >> > > > > > > > > > And yes, there's loads of in-kernel examples of doing this wrong, I've >> > > > > > > > > > been working on fixing that up, look at the patches now in Linus's tree >> > > > > > > > > > for platform and USB drivers that do this as examples of how to do it >> > > > > > > > > > right. >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > > Agreed, this patch should not be used as an approval for any crazy >> > > > > > > > > attributes; but it's necessary in order to extend the soc device's >> > > > > > > > > attributes, per the current design. >> > > > > > > > >> > > > > > > > Wait, no, let's not let the "current design" remain if it is broken! >> > > > > > > > >> > > > > > > > Why can't the soc driver handle the attributes properly so that the >> > > > > > > > individual driver doesn't have to do the create/remove? >> > > > > > > > >> > > > > > > >> > > > > > > The custom attributes that these drivers want to add to the common ones >> > > > > > > are known in advance, so I presume we could have them passed into >> > > > > > > soc_device_register() and registered together with the common >> > > > > > > attributes... >> > > > > > > >> > > > > > > It sounds like it's worth a prototype. >> > > > > > >> > > > > > Do you have an in-kernel example I can look at to get an idea of what is >> > > > > > needed here? >> > > > > > >> > > > > >> > > > > realview_soc_probe(), in drivers/soc/versatile/soc-realview.c, >> > > > > implements the current mechanism of acquiring the soc's struct device >> > > > > and then issuing a few device_create_file calls on that. >> > > > >> > > > That looks to be a trivial driver to fix up. Look at 6d03c140db2e >> > > > ("USB: phy: fsl-usb: convert platform driver to use dev_groups") as an >> > > > example of how to do this. >> > > > >> > > >> > > The difference between the two cases is that in the fsl-usb case it's >> > > attributes of the device itself, while in the soc case the >> > > realview-soc >> > > driver (or the others doing this) calls soc_device_register() to >> > > register a new (dangling) soc device, which it then adds its >> > > attributes >> > > onto. >> > >> > That sounds really really odd. Why can't the soc device do the creation >> > "automatically" when the device is registered? The soc core should >> > handle this for the soc "drivers", that's what it is there for. >> > >> Clients are registering to soc framework using >> "soce_device_register()" >> with "soc_device_attribute". This attribute structure does not have >> all >> the sysfs fields what client are interested. Hence clients are >> handling >> their required sysfs fields in their drivers. >> https://elixir.bootlin.com/linux/v5.3/source/drivers/base/soc.c#L114 > > Then you should fix that :) If i understand, you are asking me to address additional sysfs entries from the client side using "default attribute" groups. I saw your patches about "dev_groups" usage which might be part of 5.4-rc1. If i go with above approach, i end up seeing the soc information at two different sysfs paths i.e. Is this my understanding correct?
1. /sys/devices/soc0/* 2. /sys/bus/platform/drivers/msm-socinfo/*
Couple of things which i can think of addressing this issue is: 1. Modify the soc framework APIs to pass the client side sysfs attributes. This will ensure all the soc information fall under /sys/devices/soc0/* 2. Modify "struct soc_device_attribute" and add more entries. So that we do not need to change any soc framework. Problem here is others might have a different requirement which will not be full fill if i do this.
> >> > > We can't use dev_groups, because the soc_device (soc.c) isn't >> > > actually a >> > > driver and the list of attributes is a combination of things from >> > > soc.c >> > > and e.g. soc-realview.c. >> > > >> > > But if we pass a struct attribute_group into soc_device_register() and >> > > then have that register both groups using dev.groups, this should be >> > > much cleaner at least. >> > >> > Don't you have a structure you can store these in as well? >> At present client is populating entries one-by-one >> https://android.googlesource.com/kernel/msm/+/android-7.1.0_r0.2/drivers/soc/qcom/socinfo.c#1254 > > And that is known to be broken and racy and will cause problems with > userspace. This should be fixed... I saw your explanation here about race http://kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/ > > thanks, > > greg k-h
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