On Wed, Jun 14, 2023, at 12:47, Prabhakar wrote:
> +static void ax45mp_dma_cache_inv(phys_addr_t paddr, unsigned long size)
> +{
> + unsigned long start = (unsigned long)phys_to_virt(paddr);
> + char cache_buf[2][AX45MP_CACHE_LINE_SIZE];
> + unsigned long end = start + size;
> + unsigned long old_start = start;
> + unsigned long old_end = end;
> + unsigned long line_size;
> + unsigned long flags;
> +
> + if (unlikely(start == end))
> + return;
> +
> + line_size = ax45mp_priv.ax45mp_cache_line_size;
> +
> + memset(&cache_buf, 0x0, sizeof(cache_buf));
> + start = start & (~(line_size - 1));
> + end = ((end + line_size - 1) & (~(line_size - 1)));
> +
> + local_irq_save(flags);
> + if (unlikely(start != old_start))
> + memcpy(&cache_buf[0][0], (void *)start, line_size);
> +
> + if (unlikely(end != old_end))
> + memcpy(&cache_buf[1][0], (void *)(old_end & (~(line_size - 1))),
> line_size);
> +
> + ax45mp_cpu_dcache_inval_range(start, end, line_size);
> +
> + if (unlikely(start != old_start))
> + memcpy((void *)start, &cache_buf[0][0], (old_start & (line_size -
> 1)));
> +
> + local_irq_restore(flags);
> +}
I'm not quite sure what this does, maybe some comments would help.
This looks like a novel method of preserving partial cache lines
at the beginning (but not the end?) of an unaligned area.
As far as I can tell, most dma_mapping implementations don't
even try to do that at all, but the ones that do take a different
approach by calling _wback_inv() on partial cache lines instead
of calling _inv().
I'd say this does not belong into the low-level operations
here, especially since the ZICBOM variant doesn't do this either.
Arnd
