From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from na01-bl2-obe.outbound.protection.outlook.com (mail-bl2lp0207.outbound.protection.outlook.com [207.46.163.207]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 5D08C1A0455 for ; Sat, 23 Aug 2014 04:36:47 +1000 (EST) Message-ID: <1408732591.6510.5.camel@snotra.buserror.net> Subject: Re: [PATCH] powerpc: fsl_pci: Fix PCI/PCI-X regression From: Scott Wood To: Aaron Sierra Date: Fri, 22 Aug 2014 13:36:31 -0500 In-Reply-To: <964109192.130707.1408730093575.JavaMail.zimbra@xes-inc.com> References: <1335064415.96829.1408578704825.JavaMail.zimbra@xes-inc.com> <1408655996.2395.7.camel@snotra.buserror.net> <529271512.72955.1408658076028.JavaMail.zimbra@xes-inc.com> <1408658506.2395.11.camel@snotra.buserror.net> <964109192.130707.1408730093575.JavaMail.zimbra@xes-inc.com> Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Cc: Minghuan Lian , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 2014-08-22 at 12:54 -0500, Aaron Sierra wrote: > ----- Original Message ----- > > From: "Scott Wood" > > Sent: Thursday, August 21, 2014 5:01:46 PM > > > > On Thu, 2014-08-21 at 16:54 -0500, Aaron Sierra wrote: > > > ----- Original Message ----- > > > > From: "Scott Wood" > > > > Sent: Thursday, August 21, 2014 4:19:56 PM > > > > > > > > Why wouldn't a normal PCI agent be able to bus master? > > > > > > > > -Scott > > > > > > > > > > Short answer: > > > > > > Simply because the hardware strapping for Host/Agent determines the > > > default state of the Bus Master bit in the Command register. Without > > > that bit being set, an Agent won't be able to send the PCI cycles > > > necessary to enumerate the bus. > > > > But what if the host has already set that bit before Linux boots? > > That's a very good point. I think that concern can be addressed by looking > for another telltale sign of enumeration, whether an address has been > assigned to the bridge's BAR 0 (PCSRBAR). I don't see how that's any different. The host may or may not have assigned an address. > > I understand why you need to do this -- I just don't think this is a > > reliable way of detecting that you're in that situation. How about a > > kernel command line setting? > > I'd like to avoid requiring a kernel command-line option for this. It's hardware description, so you could use a device tree property. -Scott