Messages in this thread | | | Subject | Re: [PATCH v4 6/7] ARM: NOMMU: Set ARM_DMA_MEM_BUFFERABLE for M-class cpus | From | Vladimir Murzin <> | Date | Wed, 24 May 2017 09:31:54 +0100 |
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On 23/05/17 21:33, Arnd Bergmann wrote: > On Tue, May 23, 2017 at 10:01 PM, Russell King - ARM Linux > <linux@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.
Ok. Do you want it go into commit message or option description or maybe both?
Thanks Vladimir
> > Arnd >
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