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. > 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. Bjorn
