linux-kernel - Re: [PATCH 3/3] PCI: designware-ep: Return an error when requesting a too large BAR size

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Date:   Mon, 5 Feb 2018 17:25:20 +0100
From:   Niklas Cassel <niklas.cassel@...s.com>
To:     Jingoo Han <jingoohan1@...il.com>
Cc:     'Andy Shevchenko' <andy.shevchenko@...il.com>,
        'Kishon Vijay Abraham I' <kishon@...com>,
        'Joao Pinto' <Joao.Pinto@...opsys.com>,
        'Lorenzo Pieralisi' <lorenzo.pieralisi@....com>,
        'Bjorn Helgaas' <bhelgaas@...gle.com>,
        linux-pci@...r.kernel.org,
        'Linux Kernel Mailing List' <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] PCI: designware-ep: Return an error when requesting
 a too large BAR size

On Thu, Feb 01, 2018 at 02:00:40PM -0500, Jingoo Han wrote:
> On Thursday, February 1, 2018 1:58 PM, Andy Shevchenko wrote:
> > 
> > On Thu, Feb 1, 2018 at 6:11 PM, Niklas Cassel <niklas.cassel@...s.com>
> > wrote:
> > 
> > include/linux/sizes.h:
> > 
> > +SZ_4G  0x100000000ULL
> > 
> > > +       if (size > 0x100000000ULL) {
> > 
> > #include <linux/sizes.h>
> > 
> > if (size > SZ_4G) {
> 
> I like this one for the readability.
> Thank you.
> 

I liked it too, however both variants

if (size > 0x100000000ULL) {

if (size > SZ_4G) {

result in:

drivers/pci/dwc/pcie-designware-ep.c:131:11: warning:
  comparison is always false due to limited range of data type [-Wtype-limits]

when compiling with W=1 on a platform with 32-bit size_t.


The annoying thing here is that a BAR can be 64-bit,
yet the parameter size is defined as a size_t,
so the error will only show on 32-bit and not on 64-bit.

What do you think about:

if (upper_32_bits(size)) {
	dev_err(pci->dev, "can't handle BAR larger than 4GB\n");
	return -EINVAL;
}

That should compile without warnings for both
32-bit size_t and 64-bit size_t.


Regards,
Niklas