Re: [PATCH 1/2] serial: 8250: Allow port registration without UPF_BOOT_AUTOCONF

Esben Haabendal
2019-04-29T06:28:03Z

Andy Shevchenko <andy.shevchenko@gmail.com> writes:

> On Sat, Apr 27, 2019 at 12:01 PM Esben Haabendal <esben@haabendal.dk> wrote:
>> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
>> > On Fri, Apr 26, 2019 at 06:54:05PM +0200, Esben Haabendal wrote:
>> >> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
>> >> The reason for this patch is to be able to do exactly that (set port
>> >> type and UPF_FIXED_TYPE) without having UPF_BOOT_AUTOCONF added.
>> >>
>> >> In the current serial8250_register_8250_port() there is:
>> >>
>> >> uart->port.flags = up->port.flags | UPF_BOOT_AUTOCONF;
>> >>
>> >> So, even though I set UPF_FIXED_TYPE, I get
>> >> UPF_FIXED_TYPE|UPF_BOOT_AUTOCONF.
>> >
>> > Yes.
>> >
>> >> So I need this patch.
>> >
>> > Why? I don't see any problems to have these flags set.
>>
>> The problem with having UPF_BOOT_AUTOCONF is the call to
>> serial8250_request_std_resource(). It calls request_mem_region(), which
>> fails if the MFD driver already have requested the memory region for the
>> MFD device.
>
> If it's MFD, why it requested the region for its child?
> Isn't it a bug in MFD driver?

It is a PCI driver, which calls pci_request_regions(). The PCI device
carries a lot of different functions, which uses small slices of the PCI
memory region(s). With the resources being a tree structure, I don't
think it is a bug when a parent driver requests the entire memory
region.

It would be nice if child drivers requesting memory would pass the
parent memory resource. Maybe 8250 driver could be changed to accept a
struct resource pointer instead of a simple mapbase value, allowing to
setup the resource with parent pointing to the MFD memory resource.

/Esben