On Fri, Jun 03, 2022 at 11:57:47PM +0100, Jiaxun Yang wrote: > 在2022年6月2日六月 下午5:20，Bjorn Helgaas写道：. > > > > I'd really like to have a single implementation of whatever quirk > > works around this. I don't think we should have multiple copies > > just because we assume some firmware takes care of part of this > > for us. > > > Yeah that was my idea when I was writing the present version of > workaround. However in later LS7A revisions Loongson somehow raised > MRRS for several PCIe controllers on chip to 1024 and other ports > remains to be 256. Kernel have no way to aware of this change and we > can only rely on firmware to set proper value. That's fine; we need a controller-specific way to find the limit (whether it's fixed for all versions or discovered from firmware settings or whatever). My hope is that given that controller-specific value, we can have a single quirk that works on keystone, loongson, etc. to enforce the limit on all relevant devices. Some platform firmware might do that configuration already, but it's OK if a generic quirk re-does it. I don't think it's worth having two quirks, one that does the configuration, and another that relies on firmware having done it. > I have no idea how Loongson achieved this in hardware. All those > PCIe controllers are attached under the same AXI bus should share > the same AXI to HyperTransport bridge as AXI slave behind a bus > matrix. Perhaps instead of fixing error handling of their AXI > protocol implementation they just increased the buffer size in AXI > bridge so it can accomplish larger requests at one time. > >> In keystone’s case it’s likely that their firmware won’t do such thing, so > >> their workaround shouldn’t be removed. > >> And no_inc_mrrs should be set for them to prevent device drivers modifying > >> MRRS afterwards. > > > > I have the vague impression that this issue is related to an arm64 AXI > > bus property [2] or maybe a DesignWare controller property [3], so > > this might affect several PCIe controller drivers. > > In my understanding it’s likely to be a AXI implementation issue. I know almost nothing about AXI, but this concerns me because it sounds like other drivers could be affected. Bjorn
