Re: [PATCH v2] loongarch/mm: disable WUC for pgprot_writecombine as same as ioremap_wc

[Sui Jingfeng]

Hi,


On 2023/10/10 20:26, Xi Ruoyao wrote:
> > For DMA non-coherent buffers, we should try to implement arch-specific dma_map_ops,
> > invalidate the CPU cache and flush the CPU write buffer before the device do DMA. Instead
> > of pretend to be DMA coherent for all buffers, a kernel cmdline is not a system level
> > solution for all of GPU drivers and OS release.
> IIUC this is a hardware bug of 7A1000 and 7A2000, so the proper location
> of the workaround is in the bridge chip driver.  Or am I
> misunderstanding something?


The ls2k1000 and ls2k2000 SoC (which don't use with 7A1000 and 7A2000) are also suffer form this
problem. If this is a hardware bug of 7A1000 and 7A2000, why forbidden WC mapping of pages in
system RAM?

The problem of this patch and the <16c52e503043> commit is that it forbidden all WC mappings by
default. Even pages in system RAM.