Re: [PATCH 1/2] of: platform: introduce platform data length for auxdata

[Peter Chen <peter.chen@nxp.com>]

On 20-12-10 09:38:49, Rob Herring wrote:
> On Thu, Dec 10, 2020 at 7:42 AM Peter Chen <peter.chen@kernel.org> wrote:
> >
> > From: Peter Chen <peter.chen@nxp.com>
> >
> > When a platform device is released, it frees the device platform_data
> > memory region using kfree, if the memory is not allocated by kmalloc,
> > it may run into trouble. See the below comments from kfree API.
> >
> >          * Don't free memory not originally allocated by kmalloc()
> >          * or you will run into trouble.
> >
> > For the device which is created dynamically using of_platform_populate,
> > if the platform_data is existed at of_dev_auxdata structure, the OF code
> > simply assigns the platform_data pointer to newly created device, but
> > not using platform_device_add_data to allocate one. For most of platform
> > data region at device driver, which may not be allocated by kmalloc, they
> > are at global data region or at stack region at some situations.
> 
> auxdata is a "temporary" thing for transitioning to DT which I want to
> remove. So I don't really want to see it expanded nor new users. We've
> got about a dozen arm32 platforms and 5 cases under drivers/.
> 

How to handle the below user case:
Parent device creates child device through device tree node (eg, usb/dwc3,
usb/cdns3), there are some platform quirks at parent device(vendor glue
layer) need child device (core IP device) driver to handle. The quirks
are not limited to the hardware quirk, may include the callbacks, software
flag (eg: XHCI_DEFAULT_PM_RUNTIME_ALLOW/XHCI_SKIP_PHY_INIT, at
drivers/usb/host/xhci.h)

> > +       int platform_data_length = 0;
> >         int rc = 0;
> >
> >         /* Make sure it has a compatible property */
> > @@ -378,6 +387,9 @@ static int of_platform_bus_create(struct device_node *bus,
> >         if (auxdata) {
> >                 bus_id = auxdata->name;
> >                 platform_data = auxdata->platform_data;
> > +               platform_data_length = auxdata->platform_data_length;
> > +               if (platform_data && !platform_data_length)
> > +                       pr_warn("Make sure platform_data is allocated by kmalloc\n");
> 
> Isn't this going to warn on the majority of users as static data is the norm.

This warning only triggers at the cases which driver defines auxdata and
platform_data pointer is in it. Besides, directly assign the address
of static data to device platfrom_data pointer is wrong thing, this region
will be freed using kfree at platform_device_release. Using platform_device_add_data
API is the correct thing to do that.

-- 

Thanks,
Peter Chen