[RFC/PATCH] map drivers. DCACHE option for physmap and mphysmap drivers

[Josh Boyer]

On 1/26/06, Korolev, Alexey <alexey.korolev at intel.com> wrote:
> Hi All,
>
> Some mapping drivers of linux-mtd has feature of cached mapping. This
> can improve read performance on FLASH significantly .
> I think adding the option of data cache mapping would also be helpful
> for physmap and mphysmap drivers.

Is this a read-only caching?  I know several architectures and
hardware configurations that would quickly throw a machine check if
trying to flush the cache back to flash since they don't support
bursted writes.


> ========================================================================
> =====
> diff -uNr a/drivers/mtd/maps/Kconfig b/drivers/mtd/maps/Kconfig
> --- a/drivers/mtd/maps/Kconfig 2005-12-22 15:06:38.000000000 +0300
> +++ b/drivers/mtd/maps/Kconfig 2005-12-22 15:05:24.000000000 +0300
> @@ -60,6 +60,12 @@
>     Ignore this option if you use run-time physmap configuration
>     (i.e., run-time calling physmap_configure()).
>
> +config MTD_PHYSMAP_DCACHE
> + bool "Enable dcache for flash mapping"
> + depends on MTD_PHYSMAP
> + help
> +   This option enables CPU data cache for flash mapping
> +   This improves flash read speed significantly.

I would recommend adding a dependency on ARM for all of this for now. 
As other architectures are proven to be working, they can be added.


> +#ifdef CONFIG_MTD_MULTI_PHYSMAP_DCACHE
> +        if (map->inval_cache)
> +        {
> +#ifdef CONFIG_ARM
> +           map->cached = ioremap_cached(map->phys, map->size);
> +#else
> +           map->cached = __ioremap(map->phys, map->size,
> L_PTE_CACHEABLE);
> +#endif

Gah.  The above doesn't work.  L_PTE_CACHEABLE seems to be an ARM only
flag.  And it wouldn't work on PPC for example.  That version of
__ioremap makes everything implicitly cached unless _PAGE_NO_CACHED is
passed in.

As I said before, I would make this an ARM only option for now.

> +#ifdef CONFIG_MTD_PHYSMAP_DCACHE
> +#ifdef CONFIG_ARM
> + physmap_map.cached = ioremap_cached(physmap_map.phys,
> physmap_map.size);
> +#else
> + physmap_map.cached = __ioremap(physmap_map.phys, physmap_map.size,
> L_PTE_CACHEABLE);
> +#endif

Same issues as in mphysmap.

josh