On Fri, 4 Dec 2015, Thierry Reding wrote:
On Tue, Nov 03, 2015 at 05:01:46PM -0500, Nicolas Pitre wrote:
do_div() must only be used with a u64 dividend.
Signed-off-by: Nicolas Pitre nico@linaro.org
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c index 254094ab7f..5da2aa8cc3 100644 --- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c @@ -141,9 +141,8 @@ gk20a_pllg_calc_rate(struct gk20a_clk *clk)
rate = clk->parent_rate * clk->n; divider = clk->m * pl_to_div[clk->pl];
do_div(rate, divider);
return rate / 2;
- return rate / divider / 2;
}
static int
This causes build breakage on 32-bit ARM.
Funny, because the above _fixes_ build warnings on 32-bit ARM for me.
I'm also confused by the commit message because the code that I'm looking at has u64 rate and u32 divider,
If I look at drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c in v4.4-rc3 between line 137 and line 147, I see this:
gk20a_pllg_calc_rate(struct gk20a_clk *clk) { u32 rate; u32 divider;
rate = clk->parent_rate * clk->n; divider = clk->m * pl_to_div[clk->pl]; do_div(rate, divider);
return rate / 2; }
So clearly both rate and divider are u32 variables and do_div() should not be used.
Here's the warning:
drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c: In function 'gk20a_pllg_calc_rate': include/asm-generic/div64.h:207:28: warning: comparison of distinct pointer types lacks a cast (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ ^ drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:144:2: note: in expansion of macro 'do_div' do_div(rate, divider); ^
The corresponding line number in vanilla v4.4-rc3 for include/asm-generic/div64.h is line 43.
Nicolas