Hi Sui Jingfeng, Am Donnerstag, dem 01.06.2023 um 00:08 +0800 schrieb Sui Jingfeng: > Hi, > > On 2023/5/31 03:02, Bjorn Helgaas wrote: > > On Wed, May 31, 2023 at 12:06:42AM +0800, Sui Jingfeng wrote: > > > This patch adds PCI driver support on top of what already have. Take the > > > GC1000 in LS7A1000/LS2K1000 as the first instance of the PCI device driver. > > > There is only one GPU core for the GC1000 in the LS7A1000 and LS2K1000. > > > Therefore, component frameworks can be avoided. Because we want to bind the > > > DRM driver service to the PCI driver manually. > > > + * Loongson Mips and LoongArch CPU(ls3a5000, ls3a4000, ls2k1000la) > > > + * maintain cache coherency by hardware > > > + */ > > > + if (IS_ENABLED(CONFIG_CPU_LOONGSON64) || IS_ENABLED(CONFIG_LOONGARCH)) > > > + priv->has_cached_coherent = true; > > This looks like something that should be a runtime check, not a > > compile-time check. > > > > If it's possible to build a single kernel image that runs on Loongson > > MIPS or LoongArch CPU and, in addition, runs on other platforms, you > > cannot assume that all the others maintain this cache coherency. > > Nice catch! I don't even realize this! > > > LS3A4000 is mips64r2 with MSA SIMD, while LS3A5000 is LoongArch, > > instruction set, compiler, and binary interface are totally changed. > > Therefore, it's impossible to build a single kernel image that runs on > all Loongson CPUs. > > Currently, I can guarantee that this works on the Loongson platform. > > My initial intent here is to let priv->has_cached_coherent be *true* on > the Loongson platform (both mips and loongarch). > > I do know there are some other vendors who bought GPU IP from Vivante. > > say GC7000, and integrate it into their discrete GPU product. > > But it is also a PCI device, but this is another story; it deserves > another patch. > > I don't know if Etnaviv folk find some similar hardware on Arm Arch, > > Some Arm CPUs do not maintain cached coherency on hardware. > > The has_cached_coherent member can be set to false on such hardware. > > For us, it seems that there is no need to do runtime checking, > > because they are all cached coherent by default. > > > Can I improve this in the future, currently I don't have a good idea. I think I mentioned before that this needs to be a runtime check. What does dev_is_dma_coherent() return for the Vivante GPU device on your platform? Regards, Lucas
