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

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Message-ID: <87zhnpkzvj.fsf@haabendal.dk>
Date:   Tue, 14 May 2019 14:02:40 +0200
From:   Esben Haabendal <esben@...bendal.dk>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
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

Andy Shevchenko <andy.shevchenko@...il.com> writes:

> On Tue, May 14, 2019 at 12:23 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
>> On Tue, May 14, 2019 at 10:24 AM Esben Haabendal <esben@...bendal.dk> wrote:
>
>> > 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?
>
> They do not request resources by the way.

Actually, that looks like a bug in ioc3.c driver.

It is using mfd_add_devices() with a mem_base that has not been properly
requested, and the platform_get_resource() calls made by child drivers
does not guarantee exclusive access to the memory resources, as they are
not inserted in the root memory resource tree.

> You may do the same, I told you this several times.

In drivers/mfd/ioc3.c:

First, the uart resources are defined.  The register memory resource is
defined relative to the mfd driver memory resource.

+static struct resource ioc3_uarta_resources[] = {
+	DEFINE_RES_MEM(offsetof(struct ioc3, sregs.uarta),
+		       sizeof_field(struct ioc3, sregs.uarta)),
+	DEFINE_RES_IRQ(6)
+};

This is then used when creating the uart cell.

+		cell->name = "ioc3-serial8250";
+		cell->id = ioc3_serial_id++;
+		cell->resources = ioc3_uarta_resources;
+		cell->num_resources = ARRAY_SIZE(ioc3_uarta_resources);

Finally, the mfd_add_devices() call is made, giving the resource for the
BAR0 region (&ipd->pdev->resource[0]) as mem_base argument:

+	mfd_add_devices(&ipd->pdev->dev, -1, ioc3_mfd_cells,
+			cell - ioc3_mfd_cells, &ipd->pdev->resource[0],
+			0, ipd->domain);

This is just what I want to do.

But in order to guarantee exclusive access to the memory resource, I
need to have it requested.

/Esben