Am 2020-06-19 18:54, schrieb Horia Geantă:
On 6/19/2020 7:37 PM, Horia Geanta wrote:
On 6/17/2020 11:48 PM, Michael Walle wrote:
Am 2020-06-17 21:15, schrieb Horia Geantă:
On 6/4/2020 6:48 PM, Michael Walle wrote:
- desc = memalign(ARCH_DMA_MINALIGN, desc_size);
- if (!desc) {
debug("cannot allocate RNG init descriptor memory\n");return -ENOMEM;- }
- for (sh_idx = 0; sh_idx < RNG4_MAX_HANDLES; sh_idx++) {
/** If the corresponding bit is set, then it means the state* handle was initialized by us, and thus it needs to be* deinitialized as well*/if (state_handle_mask & RDSTA_IF(sh_idx)) {/** Create the descriptor for deinstantating this state* handle.*/inline_cnstr_jobdesc_rng_deinstantiation(desc, sh_idx);flush_dcache_range((unsigned long)desc,(unsigned long)desc + desc_size);Shouldn't this be roundup(desc_size, ARCH_DMA_MINALIGN) instead of desc_size?
I've seen the same idioms sometimes, but it wasn't clear to me why that would be needed; the hardware only uses the desc_size, right?
Yes, HW will use only [desc, desc + desc_size].
I think this is needed to avoid cacheline sharing issues on non-coherent platforms: CPU needs to make sure a larger area is written back to memory and corresponding cache lines are invalidated.
Looking at flush_dcache_range() implementation, it does its own rounding, based on CTR_EL0[DminLine] - "smallest data cache line size". I guess this value might be smaller than ARCH_DMA_MINALIGN, hence the explicit rounding to ARCH_DMA_MINALIGN is needed.
Btw, I think desc = memalign(ARCH_DMA_MINALIGN, desc_size); needs to be replaced with desc = malloc_cache_aligned(desc_size);
But then the rounding is not needed, right? I mean there can't be any other malloc() which might allocate memory in the same cache line.
-michael