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

Andy Shevchenko
2019-04-27T16:41:24Z

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?

> 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