On 3/26/2020 1:48 PM, Bjorn Helgaas wrote: > On Thu, Mar 26, 2020 at 01:27:36PM -0700, Ray Jui wrote: >> On 3/26/2020 12:48 PM, Bjorn Helgaas wrote: >>> ... >>> It's outside the scope of this patch, but I'm not really a fan of the >>> pcie->reg_offsets[] scheme this driver uses to deal with these >>> differences. There usually seems to be *something* that keeps the >>> driver from referencing registers that don't exist, but it doesn't >>> seem like the mechanism is very consistent or robust: >>> >>> - IPROC_PCIE_LINK_STATUS is implemented by PAXB but not PAXC. >>> iproc_pcie_check_link() avoids using it if "ep_is_internal", which >>> is set for PAXC and PAXC_V2. Not an obvious connection. >>> >>> - IPROC_PCIE_CLK_CTRL is implemented for PAXB and PAXC_V1, but not >>> PAXC_V2. iproc_pcie_perst_ctrl() avoids using it ep_is_internal", >>> so it *doesn't* use it for PAXC_V1, which does implement it. >>> Maybe a bug, maybe intentional; I can't tell. >>> >>> - IPROC_PCIE_INTX_EN is only implemented by PAXB (not PAXC), but >>> AFAICT, we always call iproc_pcie_enable() and rely on >>> iproc_pcie_write_reg() silently drop the write to it on PAXC. >>> >>> - IPROC_PCIE_OARR0 is implemented by PAXB and PAXB_V2 and used by >>> iproc_pcie_map_ranges(), which is called if "need_ob_cfg", which >>> is set if there's a "brcm,pcie-ob" DT property. No clear >>> connection to PAXB. >>> >>> I think it would be more readable if we used a single variant >>> identifier consistently, e.g., the "pcie->type" already used in >>> iproc_pcie_msi_steer(), or maybe a set of variant-specific function >>> pointers as pcie-qcom.c does. >> >> It is not possible to use a single variant identifier consistently, >> i.e., 'pcie->type'. Many of these features are controller revision >> specific, and certain revisions of the controllers may all have a >> certain feature, while other revisions of the controllers do not. In >> addition, there are overlap in features across different controllers. >> >> IMO, it makes sense to have feature specific flags or booleans, and have >> those features enabled or disabled based on 'pcie->type', which is what >> the current driver does, but like you pointed out, what the driver >> failed is to do this consistently. > > There are several drivers that have the same problem of dealing with > different revisions of hardware. It would be nice to do it in a > consistent style, whatever that is. > Sure, agree with you that it should be handled in a consistent way within this driver, and the current driver is not handling this consistently. >> The IPROC_PCIE_INTX_EN example you pointed out is a good example. I >> agree with you that we shouldn't rely on iproc_pcie_write_reg to >> silently drop the operation for PAXC. We should add code to make it >> explictly obvious that legacy interrupt is not supported in all PAXC >> controllers. >> >> pcie->pcie->reg_offsets[] scheme was not intended to be used to silently >> drop register access that are activated based on features. It's a >> mistake that should be fixed if some code in the driver is done that >> way, as you pointed out. > > That's actually why I dug into this a bit -- the > iproc_pcie_reg_is_invalid() case is really a design-time error, so it > seemed like there should be a WARN() there instead of silently > returning 0 or ignoring a write. > I think 'iproc_pcie_reg_is_invalid' is a fall back protection. We should aim to prevent this from happening in the first place using whatever means we determined appropriate, and do that consistently. In addition, I also agree with you that there should be a WARN instead of silently returning zero (for reads) and dropping the writes. We'll be looking into improving this as you suggested when we have a chance. In the mean time, I think both of us agree this is out of the scope of the issue that this patch is trying to fix, which is actually a pretty critical issue that can cause potential corruption of memory and the fix should be picked up ASAP (and for older LTS kernels too). Thanks, Ray > Bjorn >
