linux-kernel - Re: [PATCH] serial: 8250: Add support for using platform

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Date:   Tue, 14 May 2019 12:23:33 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Esben Haabendal <esben@...bendal.dk>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Lee Jones <lee.jones@...aro.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Enrico Weigelt <lkml@...ux.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Darwin Dingel <darwin.dingel@...iedtelesis.co.nz>,
        Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        He Zhe <zhe.he@...driver.com>, Marek Vasut <marex@...x.de>,
        Douglas Anderson <dianders@...omium.org>,
        Paul Burton <paul.burton@...s.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serial: 8250: Add support for using platform_device resources

On Tue, May 14, 2019 at 10:24 AM Esben Haabendal <esben@...bendal.dk> wrote:
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:
> > On Tue, May 07, 2019 at 02:22:18PM +0200, Esben Haabendal wrote:

> We are on repeat here.  I don't agree with you here.  I have a simple
> generic 8250 (16550A) compatible device, and cannot use it in a mfd
> driver using the standard mfd-core framework.

> The lacking of support for platform_get_resource() in the generic
> serial8250 driver is not a feature.  It should be supported, just as it
> is in several of the specialized 8250 drivers.

We are going circles here.
What exactly prevents you to use it? Presence of request_mem_region()?

> It would still mean that I would have revert to not using convenient and
> otherwise fully appropriate API calls like pci_request_regions() and
> mfd_add_devices().

Yes, here is the issue. 8250 requires the parent not to *request*
resources. Because child handles IO access itself.

> The mfd driver in question is for a PCI device.  Not being able to
> request the PCI regions seems silly.

Nope. Otherwise, the parent which *doesn't handle* IO on behalf of
child should not request its resources.

> Not being able to register all child devices with the call introduced
> for that sole purpose also seems silly.

> Please take a look at https://lkml.org/lkml/2019/4/9/576
> ("[PATCH v2 2/4] mfd: ioc3: Add driver for SGI IOC3 chip")

Thank you for this link.
Now, look at this comment:

+ /*
+ * Map all IOC3 registers.  These are shared between subdevices
+ * so the main IOC3 module manages them.
+ */

Is it your case? Can we see the code?

-- 
With Best Regards,
Andy Shevchenko