From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Wed, 24 Nov 2010 15:35:50 +0000 Subject: [PATCH] ARM: V6 MPCore v6_dma_inv_range RWFO fix In-Reply-To: <20101124151015.GE31572@mvista.com> References: <20101123222806.GA22936@mvista.com> <20101123224237.GF26510@n2100.arm.linux.org.uk> <1290595333.3056.6.camel@e102109-lin.cambridge.arm.com> <20101124151015.GE31572@mvista.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 24 November 2010 15:10, George G. Davis wrote: > On Wed, Nov 24, 2010 at 10:42:13AM +0000, Catalin Marinas wrote: >> On Tue, 2010-11-23 at 22:42 +0000, Russell King - ARM Linux wrote: >> > On Wed, Nov 24, 2010 at 01:28:06AM +0300, Valentine Barshak wrote: >> > > Cache ownership must be acqired by reading/writing data from the >> > > cache line to make cache operation have the desired effect on the >> > > SMP MPCore CPU. However, the ownership is never aquired in the >> > > v6_dma_inv_range function when cleaning the first line and >> > > flushing the last one, in case the address is not aligned >> > > to D_CACHE_LINE_SIZE boundary. >> > > Fix this by reading/writing data if needed, before performing >> > > cache operations. >> > >> > You should do this on the data _inside_ the requested buffer. ?We don't >> > know if the overlapping cache line shares itself with some atomic >> > variable, and doing a read-write on it could undo other updates to it. >> >> We could just use the boundary addresses to avoid writing beyond the >> buffer. Something like below (pretty much moving the BIC after the RFO, >> untested): >> >> >> diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S >> index 99fa688..d63bb55 100644 >> --- a/arch/arm/mm/cache-v6.S >> +++ b/arch/arm/mm/cache-v6.S >> @@ -204,6 +204,10 @@ ENTRY(v6_flush_kern_dcache_area) >> ? */ >> ?v6_dma_inv_range: >> ? ? ? tst ? ? r0, #D_CACHE_LINE_SIZE - 1 >> +#ifdef CONFIG_DMA_CACHE_RWFO >> + ? ? ldrne ? r2, [r0] ? ? ? ? ? ? ? ? ? ? ? ?@ read for ownership >> + ? ? strne ? r2, [r0] ? ? ? ? ? ? ? ? ? ? ? ?@ write for ownership > > My concern doing RWFO prior to aligning "start" is that it could be > non-word-aligned which may result in an alignment fault. True. Maybe you can use ldrbne/strbne. -- Catalin