Re: [PATCH] serial: 8250: Add support for using platform_device resources

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Esben Haabendal <esben@haabendal.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Lee Jones <lee.jones@linaro.org>,
	"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
	Enrico Weigelt <lkml@metux.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Darwin Dingel <darwin.dingel@alliedtelesis.co.nz>,
	Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	He Zhe <zhe.he@windriver.com>, Marek Vasut <marex@denx.de>,
	Douglas Anderson <dianders@chromium.org>,
	Paul Burton <paul.burton@mips.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] serial: 8250: Add support for using platform_device resources
Date: Tue, 14 May 2019 12:23:33 +0300	[thread overview]
Message-ID: <CAHp75VfrP6SLVzmp6LepN7dU1c7QYxfRDRtj7dCTuWzmYp2tCA@mail.gmail.com> (raw)
In-Reply-To: <87k1etmrfk.fsf@haabendal.dk>

On Tue, May 14, 2019 at 10:24 AM Esben Haabendal <esben@haabendal.dk> wrote:
> Andy Shevchenko <andriy.shevchenko@linux.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