From mboxrd@z Thu Jan 1 00:00:00 1970 From: benh@kernel.crashing.org (Benjamin Herrenschmidt) Date: Mon, 10 Apr 2017 07:41:32 +1000 Subject: [PATCH v4 19/23] drivers/fsi: Add GPIO based FSI master In-Reply-To: <5344146a-f450-7959-4688-a83ee022574b@linux.vnet.ibm.com> References: <20170329174340.89109-1-cbostic@linux.vnet.ibm.com> <20170329174340.89109-20-cbostic@linux.vnet.ibm.com> <0e1bcf3a-e8d7-9f50-bdf7-2a1e7466665b@linux.vnet.ibm.com> <1490907014.3177.207.camel@kernel.crashing.org> <93b21624-11fc-b71b-aa78-6cb4371c87ae@linux.vnet.ibm.com> <1491344360.4166.68.camel@kernel.crashing.org> <5344146a-f450-7959-4688-a83ee022574b@linux.vnet.ibm.com> Message-ID: <1491774092.4166.195.camel@kernel.crashing.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sun, 2017-04-09 at 16:22 -0500, Christopher Bostic wrote: > A 3 microsecond delay is required, however, to prevent occasional issues? > during heavy FSI bus load stress testing. > A 1 nanosecond delay using ndelay(1) had been specified prior to this? > but after looking more closely at real time performance it turned out to? > actually be roughly 1-2 microseconds.?? This appears to be the minimum? > resolution using the delay() linux libraries on the AST2400/2500.??? > Given this, increasing delay to 3 microseconds doesn't impact? > performance much considering I can now remove the sample input delay? > based on your recommendations to re-order the two clock delays. This is huge delays. We should consider a AST2xxx specific variant of the backend that uses nops or similar lab-calibrated constructs instead. Otherwise we are stuck in the kHz range, this is a >200Mhz bus :) I don't understand why 3us delay would thus be necessary. Where about did you observe issues ? Could it be that you don't wait long enough in the transitions from write to read ? Cheers, Ben. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [PATCH v4 19/23] drivers/fsi: Add GPIO based FSI master Date: Mon, 10 Apr 2017 07:41:32 +1000 Message-ID: <1491774092.4166.195.camel@kernel.crashing.org> References: <20170329174340.89109-1-cbostic@linux.vnet.ibm.com> <20170329174340.89109-20-cbostic@linux.vnet.ibm.com> <0e1bcf3a-e8d7-9f50-bdf7-2a1e7466665b@linux.vnet.ibm.com> <1490907014.3177.207.camel@kernel.crashing.org> <93b21624-11fc-b71b-aa78-6cb4371c87ae@linux.vnet.ibm.com> <1491344360.4166.68.camel@kernel.crashing.org> <5344146a-f450-7959-4688-a83ee022574b@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <5344146a-f450-7959-4688-a83ee022574b@linux.vnet.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Christopher Bostic , Joel Stanley Cc: Mark Rutland , devicetree@vger.kernel.org, Andrew Jeffery , Greg KH , Russell King , rostedt@goodmis.org, Linux Kernel Mailing List , Rob Herring , Jeremy Kerr , "Edward A . James" , Alistair Popple , mingo@redhat.com, linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org T24gU3VuLCAyMDE3LTA0LTA5IGF0IDE2OjIyIC0wNTAwLCBDaHJpc3RvcGhlciBCb3N0aWMgd3Jv dGU6Cj4gQSAzIG1pY3Jvc2Vjb25kIGRlbGF5IGlzIHJlcXVpcmVkLCBob3dldmVyLCB0byBwcmV2 ZW50IG9jY2FzaW9uYWwgaXNzdWVzwqAKPiBkdXJpbmcgaGVhdnkgRlNJIGJ1cyBsb2FkIHN0cmVz cyB0ZXN0aW5nLgo+IEEgMSBuYW5vc2Vjb25kIGRlbGF5IHVzaW5nIG5kZWxheSgxKSBoYWQgYmVl biBzcGVjaWZpZWQgcHJpb3IgdG8gdGhpc8KgCj4gYnV0IGFmdGVyIGxvb2tpbmcgbW9yZSBjbG9z ZWx5IGF0IHJlYWwgdGltZSBwZXJmb3JtYW5jZSBpdCB0dXJuZWQgb3V0IHRvwqAKPiBhY3R1YWxs eSBiZSByb3VnaGx5IDEtMiBtaWNyb3NlY29uZHMuwqDCoCBUaGlzIGFwcGVhcnMgdG8gYmUgdGhl IG1pbmltdW3CoAo+IHJlc29sdXRpb24gdXNpbmcgdGhlIGRlbGF5KCkgbGludXggbGlicmFyaWVz IG9uIHRoZSBBU1QyNDAwLzI1MDAuwqDCoMKgCj4gR2l2ZW4gdGhpcywgaW5jcmVhc2luZyBkZWxh eSB0byAzIG1pY3Jvc2Vjb25kcyBkb2Vzbid0IGltcGFjdMKgCj4gcGVyZm9ybWFuY2UgbXVjaCBj b25zaWRlcmluZyBJIGNhbiBub3cgcmVtb3ZlIHRoZSBzYW1wbGUgaW5wdXQgZGVsYXnCoAo+IGJh c2VkIG9uIHlvdXIgcmVjb21tZW5kYXRpb25zIHRvIHJlLW9yZGVyIHRoZSB0d28gY2xvY2sgZGVs YXlzLgoKVGhpcyBpcyBodWdlIGRlbGF5cy4gV2Ugc2hvdWxkIGNvbnNpZGVyIGEgQVNUMnh4eCBz cGVjaWZpYyB2YXJpYW50IG9mCnRoZSBiYWNrZW5kIHRoYXQgdXNlcyBub3BzIG9yIHNpbWlsYXIg bGFiLWNhbGlicmF0ZWQgY29uc3RydWN0cwppbnN0ZWFkLiBPdGhlcndpc2Ugd2UgYXJlIHN0dWNr IGluIHRoZSBrSHogcmFuZ2UsIHRoaXMgaXMgYSA+MjAwTWh6IGJ1cwo6KQoKSSBkb24ndCB1bmRl cnN0YW5kIHdoeSAzdXMgZGVsYXkgd291bGQgdGh1cyBiZSBuZWNlc3NhcnkuCgpXaGVyZSBhYm91 dCBkaWQgeW91IG9ic2VydmUgaXNzdWVzID8gQ291bGQgaXQgYmUgdGhhdCB5b3UgZG9uJ3Qgd2Fp dApsb25nIGVub3VnaCBpbiB0aGUgdHJhbnNpdGlvbnMgZnJvbSB3cml0ZSB0byByZWFkID8KCkNo ZWVycywKQmVuLgoKX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X18KbGludXgtYXJtLWtlcm5lbCBtYWlsaW5nIGxpc3QKbGludXgtYXJtLWtlcm5lbEBsaXN0cy5p bmZyYWRlYWQub3JnCmh0dHA6Ly9saXN0cy5pbmZyYWRlYWQub3JnL21haWxtYW4vbGlzdGluZm8v bGludXgtYXJtLWtlcm5lbAo= From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752747AbdDIWnA (ORCPT ); Sun, 9 Apr 2017 18:43:00 -0400 Received: from gate.crashing.org ([63.228.1.57]:53141 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752602AbdDIWm7 (ORCPT ); Sun, 9 Apr 2017 18:42:59 -0400 Message-ID: <1491774092.4166.195.camel@kernel.crashing.org> Subject: Re: [PATCH v4 19/23] drivers/fsi: Add GPIO based FSI master From: Benjamin Herrenschmidt To: Christopher Bostic , Joel Stanley Cc: Rob Herring , Mark Rutland , Russell King , rostedt@goodmis.org, mingo@redhat.com, Greg KH , devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Linux Kernel Mailing List , Andrew Jeffery , Alistair Popple , "Edward A . James" , Jeremy Kerr Date: Mon, 10 Apr 2017 07:41:32 +1000 In-Reply-To: <5344146a-f450-7959-4688-a83ee022574b@linux.vnet.ibm.com> References: <20170329174340.89109-1-cbostic@linux.vnet.ibm.com> <20170329174340.89109-20-cbostic@linux.vnet.ibm.com> <0e1bcf3a-e8d7-9f50-bdf7-2a1e7466665b@linux.vnet.ibm.com> <1490907014.3177.207.camel@kernel.crashing.org> <93b21624-11fc-b71b-aa78-6cb4371c87ae@linux.vnet.ibm.com> <1491344360.4166.68.camel@kernel.crashing.org> <5344146a-f450-7959-4688-a83ee022574b@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-1.fc25) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2017-04-09 at 16:22 -0500, Christopher Bostic wrote: > A 3 microsecond delay is required, however, to prevent occasional issues  > during heavy FSI bus load stress testing. > A 1 nanosecond delay using ndelay(1) had been specified prior to this  > but after looking more closely at real time performance it turned out to  > actually be roughly 1-2 microseconds.   This appears to be the minimum  > resolution using the delay() linux libraries on the AST2400/2500.    > Given this, increasing delay to 3 microseconds doesn't impact  > performance much considering I can now remove the sample input delay  > based on your recommendations to re-order the two clock delays. This is huge delays. We should consider a AST2xxx specific variant of the backend that uses nops or similar lab-calibrated constructs instead. Otherwise we are stuck in the kHz range, this is a >200Mhz bus :) I don't understand why 3us delay would thus be necessary. Where about did you observe issues ? Could it be that you don't wait long enough in the transitions from write to read ? Cheers, Ben.