[U-Boot] [PATCH v3 0/1] dm: usb: Copy over usb_device values from usb_scan_device() to final usb_device

[Hans de Goede]

Hi,

On 04-05-15 19:22, Simon Glass wrote:
> Hi Hans,
>
> On 4 May 2015 at 11:19, Hans de Goede <hdegoede at redhat.com> wrote:
>> Hi Simon,
>>
>> Here is v3 of my patch to fix the maxpacketsize0 not being set issue I
>> found and related issues.
>>
>> I've added a big fat comment to explain that the usb_device pointer is a
>> hack and should not be used outside of usb-uclass.c as requested.
>>
>> I hope this version is to your liking and you can ack it.
>>
>> Assuming that you do ack it, then my entire dm-usb fixes + ehci set is
>> all acked, and the question becomes how to take uit upstream, I can take
>> the entire set upstream through the sunxi tree, or you can take it
>> upstream through the dm tree. Let me know which way you prefer to move
>> forward with this.
>
> I should probably take it through DM. I'll do a pull request once the
> x86 pull request goes in.

Ack.

> But I'm still not sure how it is safe to pass a pointer to a local
> stack variable out through another function. Can you please explain
> that?

A function 'a' can safely pass a pointer to an on stack variable to
a function 'b' which it calls, since it is the caller of function 'b',
and as long as code from 'b' is execution we are still within the
lifetime of function 'a' (function 'a' will only end after b has
returned) and as long as execution is within the lifetime of function
'a' any on stack variables of function 'a' are valid.

AFAICT usb_child_pre_probe() gets called from the device_probe()
call inside usb_scan_device() so using a pointer to an on stack
variable of usb_scan_device() is valid since we are still executing
within the lifetime of usb_scan_device().

Hope this helps to follow my reasoning.

Regards,

Hans





>
> Regards,
> Simon
>