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

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Date:   Tue, 14 May 2019 15:42:41 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Esben Haabendal <esben@...bendal.dk>
Cc:     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 02:02:40PM +0200, Esben Haabendal wrote:
> 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.

Nope. This is the right thing to do.

> 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.

Should platform_get_resource() guarantee that? I think no, otherwise entire MFD
and other logic will collapse.

> > 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.

Here the root of our misunderstanding each other.

Every driver till now works fine and entire model works fine without resources
being requested.

I told you already that if you want your way that has to be done not in 8250
driver, but in generic code (driver core or even resource framework).

-- 
With Best Regards,
Andy Shevchenko