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Date:   Mon, 29 Apr 2019 08:27:56 +0200
From:   Esben Haabendal <>
To:     Andy Shevchenko <>
Cc:     Andy Shevchenko <>,
        "open list\:SERIAL DRIVERS" <>,
        Greg Kroah-Hartman <>,
        Jiri Slaby <>,
        Darwin Dingel <>,
        He Zhe <>,
        Jisheng Zhang <>,
        Sebastian Andrzej Siewior <>,
        Linux Kernel Mailing List <>
Subject: Re: [PATCH 1/2] serial: 8250: Allow port registration without UPF_BOOT_AUTOCONF

Andy Shevchenko <> writes:

> On Sat, Apr 27, 2019 at 12:01 PM Esben Haabendal <> wrote:
>> Andy Shevchenko <> writes:
>> > On Fri, Apr 26, 2019 at 06:54:05PM +0200, Esben Haabendal wrote:
>> >> Andy Shevchenko <> 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
>> >
>> > 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

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.


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