Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example

2018-03-28 Thread Peter Zijlstra
On Wed, Mar 28, 2018 at 10:57:11AM -0700, Tony Luck wrote: > On Wed, Mar 28, 2018 at 6:02 AM, Sinan Kaya wrote: > > +linux-ia64 > > Does IA64 follow this requirement? If not, is implementation planned? > > > > "no wmb() before writel()" > > > > Linus asked us to get rid of wmb() in front of writel

Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example

2018-03-28 Thread Tony Luck
On Wed, Mar 28, 2018 at 6:02 AM, Sinan Kaya wrote: > +linux-ia64 > Does IA64 follow this requirement? If not, is implementation planned? > > "no wmb() before writel()" > > Linus asked us to get rid of wmb() in front of writel() for UC memory. > Just checking that we are not breaking anything for I

Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example

2018-03-28 Thread Sinan Kaya
+linux-ia64 On 3/27/2018 11:02 AM, Paul E. McKenney wrote: > On Tue, Mar 27, 2018 at 02:11:27PM +0100, Will Deacon wrote: >> The section of memory-barriers.txt that describes the dma_Xmb() barriers >> has an incorrect example claiming that a wmb() is required after writing >> to coherent memory in

Re: [PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example

2018-03-27 Thread Paul E. McKenney
On Tue, Mar 27, 2018 at 02:11:27PM +0100, Will Deacon wrote: > The section of memory-barriers.txt that describes the dma_Xmb() barriers > has an incorrect example claiming that a wmb() is required after writing > to coherent memory in order for those writes to be visible to a device > before a subs

[PATCH] docs/memory-barriers.txt: Fix broken DMA vs MMIO ordering example

2018-03-27 Thread Will Deacon
The section of memory-barriers.txt that describes the dma_Xmb() barriers has an incorrect example claiming that a wmb() is required after writing to coherent memory in order for those writes to be visible to a device before a subsequent MMIO access using writel() can reach the device. In fact, thi