> From: Greg Kroah-Hartman <gre...@linuxfoundation.org> > Sent: Monday, November 9, 2020 8:05 PM > > On Mon, Nov 09, 2020 at 11:55:46AM +0000, Aisheng Dong wrote: > > > From: Greg Kroah-Hartman <gre...@linuxfoundation.org> > > > Sent: Monday, November 9, 2020 7:41 PM > > > > > > On Mon, Nov 09, 2020 at 10:57:05AM +0000, Aisheng Dong wrote: > > > > Hi Greg, > > > > > > > > > From: Greg Kroah-Hartman <gre...@linuxfoundation.org> > > > > > Sent: Monday, November 9, 2020 6:37 PM > > > > > Subject: Re: [PATCH RESEND] driver core: export > > > > > device_is_bound() to fix build failure > > > > > > > > > > On Mon, Nov 09, 2020 at 10:14:46AM +0000, Sudip Mukherjee wrote: > > > > > > Hi Greg, > > > > > > > > > > > > On Sun, Nov 8, 2020 at 8:23 AM Greg Kroah-Hartman > > > > > > <gre...@linuxfoundation.org> wrote: > > > > > > > > > > > > > > On Sat, Nov 07, 2020 at 10:47:27PM +0000, Sudip Mukherjee wrote: > > > > > > > > When CONFIG_MXC_CLK_SCU is configured as 'm' the build > > > > > > > > fails as it is unable to find device_is_bound(). The error > > > > > > > > being: > > > > > > > > ERROR: modpost: "device_is_bound" > [drivers/clk/imx/clk-imx-scu.ko] > > > > > > > > undefined! > > > > > > > > > > > > > > > > Export the symbol so that the module finds it. > > > > > > > > > > > > > > > > Fixes: 77d8f3068c63 ("clk: imx: scu: add two cells binding > > > > > > > > support") > > > > > > > > Signed-off-by: Sudip Mukherjee > > > > > > > > <sudipm.mukher...@gmail.com> > > > > > > > > --- > > > > > > > > > > > > > > > > resending with the Fixes: tag. > > > > > > > > > > > > > > > > drivers/base/dd.c | 1 + > > > > > > > > 1 file changed, 1 insertion(+) > > > > > > > > > > > > > > > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c index > > > > > > > > 148e81969e04..a796a57e5efb 100644 > > > > > > > > --- a/drivers/base/dd.c > > > > > > > > +++ b/drivers/base/dd.c > > > > > > > > @@ -353,6 +353,7 @@ bool device_is_bound(struct device *dev) > { > > > > > > > > return dev->p && > > > > > > > > klist_node_attached(&dev->p->knode_driver); > > > > > > > > } > > > > > > > > +EXPORT_SYMBOL(device_is_bound); > > > > > > > > > > > > > > EXPORT_SYMBOL_GPL() please, like all the other exports in this > > > > > > > file. > > > > > > > > > > > > > > Also, wait, no, don't call this, are you sure you are > > > > > > > calling it in a race-free way? And what branch/tree is the above > commit in? > > > > > > > > > > > > I have not checked fully but since it is being called from > > > > > > probe() I assume the lock will be held at that time. > > > > > > > > > > probe() should never call this function as it makes no sense at > > > > > all at that point in time. The driver should be fixed. > > > > > > > > Would you suggest if any other API we can use to allow the driver > > > > to know whether another device has been probed? > > > > > > There is none, sorry, as that just opens up way too many problems. > > > > > > > For imx scu driver in question, it has a special requirement that > > > > it depends on scu power domain driver. However, there're a huge > > > > number > > > > (200+) of power domains for each device clock, we can't define > > > > them all in DT > > > for a single clock controller node. > > > > > > > > That's why we wanted to use device_is_bound() before to check if > > > > scu power domain is ready or not to support defer probe. > > > > > > Use the device link functionality for this type of thing, that is > > > what it was created for. > > > > > > > Thanks for the suggestion. I will check it how to use. > > BTW, I wonder if dev_driver_string() could be an optional solution > > which seems a more simple way? > > Also, how do you really know you even have a valid pointer to that other > device > structure? How are you getting access to that? >
The rough idea is as follows. Not sure if those APIs are safe enough as there're many users In kernel. pd_np = of_find_compatible_node(NULL, NULL, "fsl,scu-pd"); pd_dev = of_find_device_by_node(pd_np); if (!pd_dev || !dev_driver_string(&pd_dev->dev) || strcmp(dev_driver_string(&pd_dev->dev), "imx-scu-pd")) { of_node_put(pd_np); return -EPROBE_DEFER; } const char *dev_driver_string(const struct device *dev) { struct device_driver *drv; /* dev->driver can change to NULL underneath us because of unbinding, * so be careful about accessing it. dev->bus and dev->class should * never change once they are set, so they don't need special care. */ drv = READ_ONCE(dev->driver); return drv ? drv->name : (dev->bus ? dev->bus->name : (dev->class ? dev->class->name : "")); } EXPORT_SYMBOL(dev_driver_string); Anyway, I will continue to investigate device_link according to your suggestions. Regards Aisheng > thanks, > > greg k-h