Re: [PATCH] niu: bitwise or does not imply ordering

Jesper Dangaard Brouer
2008-11-16T15:33:01Z

I have tested it on the actual hardware, it works...

I actually agree that we should make it explicit, eventhough DaveM seems
to disagree on the netdev list.

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Tested-by: Jesper Dangaard Brouer <hawk@comx.dk>

On Sun, 2008-11-16 at 15:43 -0600, Milton Miller wrote:
> commit e23a59e1ca6d177a57a7791b3629db93ff1d9813 (niu: Fix readq
> implementation when architecture does not provide one.) reordered the
> arguments to a bitwise or to change the emitted code. However, C does
> not guarantee the evaluation order.
>
> Split the line into two statements. While there, reduce some parens
> by using two variables.
>
> Signed-off-By: Milton Miller <miltonm@bga.com>
> Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
> ---
> complie tested on ppc6xx_defconfig, I have no hardware.
> making the vars u64 saves the later cast with no signficiant codegen difference
>
> Index: work.git/drivers/net/niu.c
> ===================================================================
> --- work.git.orig/drivers/net/niu.c 2008-11-16 01:34:44.000000000 -0600
> +++ work.git/drivers/net/niu.c 2008-11-16 02:59:06.000000000 -0600
> @@ -51,7 +51,18 @@ MODULE_VERSION(DRV_MODULE_VERSION);
> #ifndef readq
> static u64 readq(void __iomem *reg)
> {
> - return ((u64) readl(reg)) | (((u64) readl(reg + 4UL)) << 32);
> + u64 l, u;
> + /*
> + * The TX_CS register has counters in the upper 32-bits and state
> + * bits in the lower 32-bits. A read clears the state bits.
> + *
> + * Therefore this driver must read the lower word then the upper one
> + * when the architecture doesn't have an atomic readq.
> + */
> + l = readl(reg);
> + u = readl(reg + 4UL);
> +
> + return l | (u << 32);
> }
>
> static void writeq(u64 val, void __iomem *reg)
>
--
Med venlig hilsen / Best regards
Jesper Brouer
ComX Networks A/S
Linux Network developer
Cand. Scient Datalog / MSc.
Author of http://adsl-optimizer.dk
LinkedIn: http://www.linkedin.com/in/brouer