> From: "Stephen Boyd" <sboyd@xxxxxxxxxxxxxx>
> To: linux-sparse@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Sent: Tuesday, 25 July, 2017 9:30:20 PM
> Subject: Sparse warnings on GENMASK + arm32
>
> I see sparse warning when I check a clk driver file in the kernel
> on a 32-bit ARM build.
>
> drivers/clk/sunxi/clk-sun6i-ar100.c:65:20: warning: cast truncates bits from
> constant value (3ffffffff becomes ffffffff)
>
> The code in question looks like:
>
> static const struct factors_data sun6i_ar100_data = {
> .mux = 16,
> .muxmask = GENMASK(1, 0),
> .table = &sun6i_ar100_config,
> .getter = sun6i_get_ar100_factors,
> };
>
> where factors_data is
>
> struct factors_data {
> int enable;
> int mux;
> int muxmask;
> const struct clk_factors_config *table;
> void (*getter)(struct factors_request *req);
> void (*recalc)(struct factors_request *req);
> const char *name;
> };
>
>
> and sparse seems to be complaining about the muxmask assignment
> here. Oddly, this doesn't happen on arm64 builds. Both times, I'm
> checking this on an x86-64 machine.
>
> $ sparse --version
> v0.5.1-rc4-1-gfa71b7ac0594
>
> Is there something confusing to sparse in the GENMASK macro?
>
Hmm, it seems sparse is incorrectly taking ~0UL to be a 64-bit value
while BITS_PER_LONG is (correctly) evaluated to be 32.
#define GENMASK(h, l) \
(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
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