linux-kernel - Re: [PATCH 1/2] serial: 8250: Allow port registration without UPF_BOOT

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Date:   Sat, 27 Apr 2019 19:41:10 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Esben Haabendal <esben@...bendal.dk>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Darwin Dingel <darwin.dingel@...iedtelesis.co.nz>,
        He Zhe <zhe.he@...driver.com>,
        Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] serial: 8250: Allow port registration without UPF_BOOT_AUTOCONF

On Sat, Apr 27, 2019 at 12:01 PM Esben Haabendal <esben@...bendal.dk> wrote:
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:
> > On Fri, Apr 26, 2019 at 06:54:05PM +0200, Esben Haabendal wrote:
> >> Andy Shevchenko <andriy.shevchenko@...ux.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?

>  And I believe that is a valid thing to do.
>
> To workaround this, I first thought I could just avoid setting
> port->mapbase, causing serial8250_request_std_resource() to be a no-op.
> But this breaks with more than one UART port, as uart_match_port() will
> match the same line for all such UART ports, causing all but the last
> one to be removed.
>
> That said, the purpose of UPF_BOOT_AUTOCONF (for 8250 driver) is to
> request and map the register memory.  So when that is already done by
> the parent MFD driver, I think it is silly to workaround problems caused
> by UPF_BOOT_AUTOCONF being force setted, when it really shouldn't.


--
With Best Regards,
Andy Shevchenko