tegra210-adma: fix 32-bit x86 build

The Tegra210 Audio DMA controller driver did a plain divide:

	page_no = (res_page->start - res_base->start) / cdata->ch_base_offset;

which causes problems on 32-bit x86 configurations that have 64-bit
resource sizes:

  x86_64-linux-ld: drivers/dma/tegra210-adma.o: in function `tegra_adma_probe':
  tegra210-adma.c:(.text+0x1322): undefined reference to `__udivdi3'

because gcc doesn't generate the trivial code for a 64-by-32 divide,
turning it into a function call to do a full 64-by-64 divide.  And the
kernel intentionally doesn't provide that helper function, because 99%
of the time all you want is the narrower version.

Of course, tegra210 is a 64-bit architecture and the 32-bit x86 build is
purely for build testing, so this really is just about build coverage
failure.

But build coverage is good.

Side note: div_u64() would be suboptimal if you actually have a 32-bit
resource_t, so our "helper" for divides are admittedly making it harder
than it should be to generate good code for all the possible cases.

At some point, I'll consider 32-bit x86 so entirely legacy that I can't
find it in myself to care any more, and we'll just add the __udivdi3
library function.

But for now, the right thing to do is to use "div_u64()" to show that
you know that you are doing the simpler divide with a 32-bit number.
And the build error enforces that.

While fixing the build issue, also check for division-by-zero, and for
overflow.  Which hopefully cannot happen on real production hardware,
but the value of 'ch_base_offset' can definitely be zero in other
places.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/dma/tegra210-adma.c b/drivers/dma/tegra210-adma.c
index 6896da8ac7ef6b3cf67e8a2e1f3f28a7856ac248..5c6a5b35898732cc63d502a7153f0e2a0fe1eeb3 100644 (file)
--- a/drivers/dma/tegra210-adma.c
+++ b/drivers/dma/tegra210-adma.c
@@ -887,7 +887,7 @@ static int tegra_adma_probe(struct platform_device *pdev)
        const struct tegra_adma_chip_data *cdata;
        struct tegra_adma *tdma;
        struct resource *res_page, *res_base;
-       int ret, i, page_no;
+       int ret, i;
 
        cdata = of_device_get_match_data(&pdev->dev);
        if (!cdata) {
@@ -914,9 +914,20 @@ static int tegra_adma_probe(struct platform_device *pdev)
 
                res_base = platform_get_resource_byname(pdev, IORESOURCE_MEM, "global");
                if (res_base) {
-                       page_no = (res_page->start - res_base->start) / cdata->ch_base_offset;
-                       if (page_no <= 0)
+                       resource_size_t page_offset, page_no;
+                       unsigned int ch_base_offset;
+
+                       if (res_page->start < res_base->start)
+                               return -EINVAL;
+                       page_offset = res_page->start - res_base->start;
+                       ch_base_offset = cdata->ch_base_offset;
+                       if (!ch_base_offset)
                                return -EINVAL;
+
+                       page_no = div_u64(page_offset, ch_base_offset);
+                       if (!page_no || page_no > INT_MAX)
+                               return -EINVAL;
+
                        tdma->ch_page_no = page_no - 1;
                        tdma->base_addr = devm_ioremap_resource(&pdev->dev, res_base);
                        if (IS_ERR(tdma->base_addr))