USB mass storage and ARM cache coherency

[Catalin Marinas]

On Wed, 2010-02-24 at 21:13 +0000, Benjamin Herrenschmidt wrote:
> On Wed, 2010-02-24 at 11:19 -0500, Alan Stern wrote:
> > > It is but I'm not confident the responsibility for doing that cleanup
> > > is at the HCD level. That would impact a lot of HCD activities that
> > > don't need such flushing since the use of the page is purely in-kernel.
> >
> > That's right.  The HCD merely puts data wherever it's told to.  It
> > doesn't know whether the destination is in the page cache, in
> > userspace, or anywhere else.  The same is true for usb-storage.
> 
> I'm surprised that usb-storage has an issue here. It shouldn't afaik,
> since it's just a SCSI driver (or not anymore ?) and the BIO or
> filesystems handle things there no ? I haven't seen a single call to
> flush_dcache_page() in any of drivers/scsi, drivers/ata or drivers/ide
> when I looked...

The BIO or filesystem code don't call flush_dcache_page() either (well
some do like cramfs or jffs but they decompress the data received from
the block device).

-- 
Catalin