linux-kernel - Re: [PATCH 3/4] MIPS: Loongson64: Yeeloong add platform driver Yeeloong is a laptop with a MIPS Loongson 2F processor, AMD CS5536 chipset, and KB3310B controller.

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Date:   Tue, 14 Nov 2017 14:35:24 +0100
From:   Ralf Baechle <ralf@...ux-mips.org>
To:     jiaxun.yang@...goat.com
Cc:     linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] MIPS: Loongson64: Yeeloong add platform driver
 Yeeloong is a laptop with a MIPS Loongson 2F processor, AMD CS5536 chipset,
 and KB3310B controller.

On Sun, Nov 12, 2017 at 02:36:16PM +0800, jiaxun.yang@...goat.com wrote:

> +     asm(".set noreorder\n");
> +     /*  input enable */
> +     outl(0x00000800, (gpio_base | 0xA0));
> +     /*  revert the input */
> +     outl(0x00000800, (gpio_base | 0xA4));
> +     /*  event-int enable */
> +     outl(0x00000800, (gpio_base | 0xB8));
> +     asm(".set reorder\n");

I forgot to comment on this .set noreorder thing.  GCC expects gas to be
in reorder mode at the end of every bit of inline assembler, so above
code is at the mercy of GCC.

Not sure what the intent was here, was it to avoid GCC from reordering
the outl() calls?  These are already marked volatlile and should not be
reordered by GCC.  .set (no)reorder on the other hand is a directive
to GAS and GCC won't be influenced at all by it.

Cheers,

  Ralf