From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann 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> 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" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160602140001.GB8262@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-rockchip" Errors-To: linux-rockchip-bounces+glpar-linux-rockchip=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Bjorn Helgaas Cc: Thomas Petazzoni , Pratyush Anand , Heiko Stuebner , linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Shawn Lin , Wenrui Li , Doug Anderson , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-rockchip-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Alex Williamson , Hannes Reinecke , Jingoo Han , Bjorn Helgaas , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-rockchip.vger.kernel.org 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