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Re: [PATCH]: IP32: Enable L3 Cache on RM7000 Processor

To: Kumba <kumba@gentoo.org>
Subject: Re: [PATCH]: IP32: Enable L3 Cache on RM7000 Processor
From: Ralf Baechle <ralf@linux-mips.org>
Date: Mon, 27 Apr 2009 12:25:24 +0200
Cc: Linux MIPS List <linux-mips@linux-mips.org>
In-reply-to: <49EAA3AF.3030409@gentoo.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <49EAA3AF.3030409@gentoo.org>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.18 (2008-05-17)
On Sun, Apr 19, 2009 at 12:08:15AM -0400, Kumba wrote:

> diff -Naurp a/arch/mips/mm/sc-rm7k.c b/arch/mips/mm/sc-rm7k.c
> --- a/arch/mips/mm/sc-rm7k.c  2009-04-18 23:23:49.000000000 -0400
> +++ b/arch/mips/mm/sc-rm7k.c  2009-04-18 23:52:09.690656791 -0400
> @@ -25,11 +25,23 @@
>  /* Secondary cache parameters. */
>  #define scache_size  (256*1024)      /* Fixed to 256KiB on RM7000 */
>
> +/* Tertiary cache parameters */
> +#define tc_lsize      32
> +#ifdef CONFIG_SGI_IP32
> +#define tcache_size   (1024*1024)    /* IP32's RM7000 has 1MB L3 */
> +#else
> +#define tcache_size   (8*1024*1024)  /* 8MB (max) for all others */
> +#endif

No platform-specific #ifdefs into generic code.  More on that see below.

> +
>  extern unsigned long icache_way_size, dcache_way_size;
>
>  #include <asm/r4kcache.h>
>
> -static int rm7k_tcache_enabled;
> +static int rm7k_tcache_enabled = 0;
> +
> +static char *way_string[] __initdata = { NULL, "direct mapped", "2-way",
> +     "3-way", "4-way", "5-way", "6-way", "7-way", "8-way"
> +};
>
>  /*
>   * Writeback and invalidate the primary cache dcache before DMA.
> @@ -105,6 +117,26 @@ static __cpuinit void __rm7k_sc_enable(v
>                     :
>                     : "r" (CKSEG0ADDR(i)), "i" (Index_Store_Tag_SD));
>       }
> +
> +
> +     /* tertiary cache */
> +     set_c0_config(RM7K_CONF_TE);
> +
> +     write_c0_taglo(0);
> +     write_c0_taghi(0);
> +
> +     for (i = 0; i < tcache_size; i += tc_lsize) {
> +             __asm__ __volatile__ (
> +                   ".set noreorder\n\t"
> +                   ".set mips3\n\t"
> +                   "cache %1, (%0)\n\t"
> +                   ".set mips0\n\t"
> +                   ".set reorder"
> +                   :
> +                   : "r" (CKSEG0ADDR(i)), "i" (Page_Invalidate_T));

Use cache_op() from <asm/r4kcache.h> instead of more inline assembler.

> +     }
> +
> +     rm7k_tcache_enabled = 1;
>  }
>
>  static __cpuinit void rm7k_sc_enable(void)
> @@ -119,6 +151,12 @@ static __cpuinit void rm7k_sc_enable(voi
>  static void rm7k_sc_disable(void)
>  {
>       clear_c0_config(RM7K_CONF_SE);
> +
> +     /* tertiary cache */
> +     if (!rm7k_tcache_enabled)
> +             return;
> +
> +     clear_c0_config(RM7K_CONF_TE);
>  }

I wonder if it is safe to just disable the cache without flushing it before or
after.

>  static struct bcache_ops rm7k_sc_ops = {
> @@ -153,20 +191,20 @@ void __cpuinit rm7k_sc_init(void)
>       if (!(config & RM7K_CONF_TC)) {
>
>               /*
> -              * We can't enable the L3 cache yet. There may be board-specific
> -              * magic necessary to turn it on, and blindly asking the CPU to
> -              * start using it would may give cache errors.
> -              *
> -              * Also, board-specific knowledge may allow us to use the
> +              * Board-specific knowledge may allow us to use the
>                * CACHE Flash_Invalidate_T instruction if the tag RAM supports
>                * it, and may specify the size of the L3 cache so we don't have
> -              * to probe it.
> +              * to probe it.  For now, we set the size to 8MB, except on IP32
> +              * where we know the size is fixed at 1MB.
>                */
> -             printk(KERN_INFO "Tertiary cache present, %s enabled\n",
> -                    (config & RM7K_CONF_TE) ? "already" : "not (yet)");
> +             c->tcache.linesz = tc_lsize;
> +             c->tcache.ways = 1;
> +             c->tcache.waybit= __ffs(tcache_size / c->tcache.ways);
> +             c->tcache.waysize = tcache_size / c->tcache.ways;
> +             c->tcache.sets = tcache_size / (c->tcache.linesz * 
> c->tcache.ways);
> +             printk(KERN_INFO "Tertiary cache size %dK, %s, linesize %d 
> bytes.\n",
> +                    (tcache_size >> 10), way_string[c->tcache.ways], 
> tc_lsize);

Initializing c->tcache here is nice but it all depends on the tcache_size which
depends on the platform and isn't (I call it a design flaw) easily accessible.  
The
solution is a R4000SC-style probe for the cache size.  See c-r4.c probe_scache()
for how this works and emjoy the scary comments.  It should easier to do this 
with
just banging the cache tags on the RM7000 while the T-cache is disabled.

> -             if ((config & RM7K_CONF_TE))
> -                     rm7k_tcache_enabled = 1;
>       }
>
>       bcops = &rm7k_sc_ops;
>
>

  Ralf

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