-----Original Message----- From: Russell King - ARM Linux [mailto:linux@xxxxxxxxxxxxxxxx] Sent: Saturday, July 24, 2010 3:01 AM To: Sin, David Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxxxxx; linux-omap@xxxxxxxxxxxxxxx; Tony Lindgren; Kanigeri, Hari; Ohad Ben-Cohen; Hiremath, Vaibhav; Shilimkar, Santosh; Molnar, Lajos Subject: Re: [RFC 4/8] TILER-DMM: TILER Memory Manager interface and implementation On Fri, Jul 23, 2010 at 06:22:24PM -0500, David Sin wrote: > +/* allocate and flush a page */ > +static struct mem *alloc_mem(void) > +{ > + struct mem *m = kzalloc(sizeof(*m), GFP_KERNEL); > + if (!m) > + return NULL; > + > + m->pg = alloc_page(GFP_KERNEL | GFP_DMA); > + if (!m->pg) { > + kfree(m); > + return NULL; > + } > + > + m->pa = page_to_phys(m->pg); > + > + /* flush the cache entry for each page we allocate. */ > + dmac_flush_range(page_address(m->pg), > + page_address(m->pg) + PAGE_SIZE); > + outer_flush_range(m->pa, m->pa + PAGE_SIZE); NAK. This is an abuse of these interfaces, and is buggy in any case. ARMv6 and ARMv7 CPUs speculatively prefetch memory, which means that there's no guarantee that if you flush the caches for a particular range of virtual space, that it will stay flushed until you decide to read it. So flushing the caches in some memory allocator can't guarantee that when you eventually get around to using the page that there won't be cache lines associated with it. [dhs] Russell, thanks for reviewing this code. Do you have any interface suggestions that you can share that would make this proper? Ideally, I would like to get physical pages without associated virtual address, or ones that are non-cached/non-bufferable. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
