Re: [PATCH v3 1/2] dmaengine: tegra210-adma: Fix build error due to 64-by-32 division
From: Jon Hunter
Date: Tue Feb 04 2025 - 12:19:27 EST
On 04/02/2025 17:03, Thierry Reding wrote:
On Tue, Feb 04, 2025 at 10:13:09PM +0530, Mohan Kumar D wrote:
On 04-02-2025 21:06, Thierry Reding wrote:
On Thu, Jan 16, 2025 at 09:50:32PM +0530, Mohan Kumar D wrote:
Kernel test robot reported the build errors on 32-bit platforms due to
plain 64-by-32 division. Following build erros were reported.
"ERROR: modpost: "__udivdi3" [drivers/dma/tegra210-adma.ko] undefined!
ld: drivers/dma/tegra210-adma.o: in function `tegra_adma_probe':
tegra210-adma.c:(.text+0x12cf): undefined reference to `__udivdi3'"
This can be fixed by using lower_32_bits() for the adma address space as
the offset is constrained to the lower 32 bits
Fixes: 68811c928f88 ("dmaengine: tegra210-adma: Support channel page")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202412250204.GCQhdKe3-lkp@xxxxxxxxx/
Signed-off-by: Mohan Kumar D <mkumard@xxxxxxxxxx>
---
drivers/dma/tegra210-adma.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/drivers/dma/tegra210-adma.c b/drivers/dma/tegra210-adma.c
index 6896da8ac7ef..258220c9cb50 100644
--- a/drivers/dma/tegra210-adma.c
+++ b/drivers/dma/tegra210-adma.c
@@ -887,7 +887,8 @@ 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;
+ unsigned int page_no, page_offset;
+ int ret, i;
cdata = of_device_get_match_data(&pdev->dev);
if (!cdata) {
@@ -914,9 +915,16 @@ 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)
+ if (WARN_ON(lower_32_bits(res_page->start) <=
+ lower_32_bits(res_base->start)))
Don't we technically also want to check that
res_page->start <= res_base->start
because otherwise people might put in something that's completely out of
range? I guess maybe you could argue that the DT is then just broken,
but since we're checking anyway, might as well check for all corner
cases.
Thierry
ADMA Address range for all Tegra chip falls within 32bit range. Do you think
still we need to have this extra check which seems like redundant for now.
No, you're right. If this is all within the lower 32 bit range, this
should be plenty enough. It might be worth to make it a bit more
explicit and store these values in variables and add a comment as to
why we only need the 32 bits. That would also make the code a bit
easier to read by making the lines shorter.
// memory regions are guaranteed to be within the lower 4 GiB
u32 base = lower_32_bits(res_base->start);
u32 page = lower_32_bits(res_page->start);
if (WARN_ON(page <= base))
...
etc.
Hm... on the other hand. Do we know that it's always going to stay that
way? What if we ever get a chip that has a very different address map?
You mean a DMA register space that crosses a 4GB address boundary? I
would hope not but maybe I should not assume that!
Maybe we can do a combination of Arnd's patch and this. In conjunction
with your second patch here, this could become something along these
lines:
u64 offset, page;
if (WARN_ON(res_page->start <= res_base->start))
return -EINVAL;
offset = res_page->start - res_base->start;
page = div_u64(offset, cdata->ch_base_offset);
We were trying to avoid the div_u64 because at some point we want to
convert the result to 32-bits to avoid any further 64-bit math and we
really don't need 64-bits for the page number.
Jon
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