On Wed, 7 Jun 2023 11:17:33 +0000 "Paller, Kim Seer" <KimSeer.Paller@xxxxxxxxxx> wrote: > > -----Original Message----- > > From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > > Sent: Tuesday, June 6, 2023 6:36 PM > > To: Paller, Kim Seer <KimSeer.Paller@xxxxxxxxxx> > > Cc: Jonathan Cameron <jic23@xxxxxxxxxx>; lars@xxxxxxxxxx; > > krzysztof.kozlowski@xxxxxxxxxx; broonie@xxxxxxxxxx; lgirdwood@xxxxxxxxx; > > linux-iio@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > > Subject: Re: [PATCH v2 2/2] iio: adc: max14001: New driver > > > > [External] > > > > > > > > > > > > > > > + struct mutex lock; > > > > > + struct regmap *regmap; > > > > > + int vref_mv; > > > > > + /* > > > > > + * DMA (thus cache coherency maintenance) requires the > > > > > + * transfer buffers to live in their own cache lines. > > > > > > > > You are looking at an old kernel I guess - we fixed all of these - and > > > > introduced IIO_DMA_MINALIGN for __aligned(IIO_DMA_MINALIGN) to > > > > make it easier to fix any such problems in future. > > > > > > > > Upshot is that ___cacheline_aligned aligns to the l1 cacheline length. > > > > Some fun systems (such as the big servers I use in my dayjob) have higher > > > > cacheline sizes for their larger / further from CPU caches. > > > > One group of SoCs out there is known to both do non coherent DMA and > > > > have a larger line size for the bit relevant to that than ___cacheline_aligned > > > > gives you. So on that rare platform this is currently broken. > > > > > > It's good to know. Given this information, is there anything specific that I > > > need to change in the code or implementation related to > > > the ___cacheline_aligned part? > > > > Replace it with __aligned(IIO_DMA_MINALIGN) as has hopefully now been > > done > > in all upstream drivers. > > When I attempted to implement this change, I encountered a checkpatch warning > in the latest kernel version. The warning indicated that externs should be avoided > in .c files and emphasized the need for an identifier name for the function > definition argument 'IIO_DMA_MINALIGN'. I attempted to define a macro with an > appropriate identifier name, but I still received the same checkpatch warning. > It's possible that I may have overlooked something in my approach. I would > appreciate your thoughts and insights on this matter. Thanks. Ignore checkpatch for this one. Check patch is miss handling of __aligned. At a guess - needs an entry in this list: https://elixir.bootlin.com/linux/latest/source/scripts/checkpatch.pl#L513 Though I'm never great at understanding the perl so may have that wrong. Jonathan
