From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: From: Arnd Bergmann To: Bjorn Helgaas Cc: Bjorn Helgaas , Heiko Stuebner , Wenrui Li , Doug Anderson , linux-pci@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org, Shawn Lin , Thomas Petazzoni , linux-arm-kernel@lists.infradead.org, Jingoo Han , Pratyush Anand , Hannes Reinecke , Alex Williamson Subject: Re: [PATCH 1/3] pci: introduce read_bridge/write_bridge pci ops Date: Thu, 02 Jun 2016 17:06:55 +0200 Message-ID: <3585926.N1C2xx3GaB@wuerfel> In-Reply-To: <20160602140001.GB8262@localhost> References: <1464784332-3775650-1-git-send-email-arnd@arndb.de> <4967020.J4dsRYGugq@wuerfel> <20160602140001.GB8262@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" List-ID: On Thursday, June 2, 2016 9:00:01 AM CEST Bjorn Helgaas wrote: > > I just did a count of the implementations of pci_ops: I found 107 > > instances of 'struct pci_ops', and 67 of them treat type0 and type1 > > access differently in some form. > > > > I'd estimate that about half of them, or roughly a third of the total > > instances would benefit from my change, if we were to do them again. > > Clearly there is no need to change the existing code here when it works, > > unless the benefit is very clear and the code is actively maintained. > > > > In some cases, the difference is only that the root bus has a limited > > set of devices that are allowed to be accessed, so there would > > likely be no benefit of this, compared to e.g. yet another callback > > that checks the validity. > > Some other instances have type0 registers at a different memory location > > from type1, some use different layout inside of that space, and some > > are completely different. > > The type0/type1 distinction still seems out of place to me at the call > site. Is there any other reason a caller would care about the > difference between type0 and type1? The callers really shouldn't care, but they also shouldn't call the pci_ops function pointer (and as we found earlier, there are only three such callers). The distinction between type0 and type1 in my mind is an implementation detail of the pci_{read,write}_config_{byte,word,dword} functions that call the low-level operations here. Arnd