Re: Question about caching

[David Laight <david%l8s.co.uk@localhost>]

On Thu, Sep 10, 2009 at 09:52:37PM +0200, Michael van Elst wrote:
> 
> The 68040 manual (section 4.5) makes the following statement:
> 
> <quote>
> Because each cache line reflects page state information, a page should
> be flushed from the cache before any of the page attributes are changed.
> The presence of a valid or dirty cache line implicitely indicates that
> accesses to the page containing the line are cachable. The presence of
> a dirty cache line implies that the page is not write protected and that
> writes to the page are in copyback mode.
> </quote>
> 
> My interpretation is that changed page attributes are equivalent to
> two mappings with different attributes and that coherency is maintained.

I would interpret the above as saying that the cache line is checked
before any state info in the page tables (or TLB) that indicates
the cacheable state of the page is checked.

I'm not sure that has any relevance to whether an uncached access
will affect a cache line that refers to the same physical address
but a different virtual one.

        David

-- 
David Laight: david%l8s.co.uk@localhost