On Tue, May 23, 2017 at 10:01 PM, Russell King - ARM Linux <li...@armlinux.org.uk> wrote: > On Mon, Apr 24, 2017 at 11:16:56AM +0100, Vladimir Murzin wrote: >> Now, we have dedicated non-cacheable region for consistent DMA >> operations. However, that region can still be marked as bufferable by >> MPU, so it'd be safer to have barriers by default. > > What do you actually want here? Your patch doesn't quite make sense, > the commit description seems to indicate that you require this option > to be set for V7M, but the patch says otherwise. > >> config ARM_DMA_MEM_BUFFERABLE >> - bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K) && >> !CPU_V7 >> - default y if CPU_V6 || CPU_V6K || CPU_V7 >> + bool "Use non-cacheable memory for DMA" if (CPU_V6 || CPU_V6K || >> CPU_V7M) && !CPU_V7 > > This "if" conditional conditionalises the visibility of the option, > it doesn't conditionalise the value. > >> + default y if CPU_V6 || CPU_V6K || CPU_V7 || CPU_V7M > > Taking both of these changes together what you end up with is an option > presented to the user for "Use non-cacheable memory for DMA" which > they can choose to disable. > > If you require this option to be set, that's incorrect - your modification > to the default line is correct, but the first line is not. To achieve > that, you want the if condition to evaluate false for V7M, thereby hiding > the option from the user. In that case, the default value will always be > assigned to the option.
I had the opposite comment in the previous version ;-) https://lkml.org/lkml/2017/4/19/185 I think the current patch is correct, but the description could still be clarified: On some of the beefier ARMv7-M machines (with DMA and write buffers) we want this enabled, while those that didn't need it until now also won't need it in the future. Arnd
