From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC6D5C636CB for ; Sat, 17 Jul 2021 13:46:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C9B4C613D9 for ; Sat, 17 Jul 2021 13:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233956AbhGQNtX convert rfc822-to-8bit (ORCPT ); Sat, 17 Jul 2021 09:49:23 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]:39990 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233125AbhGQNtW (ORCPT ); Sat, 17 Jul 2021 09:49:22 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-18-c9JPzhnSOuerytt2WipVKQ-1; Sat, 17 Jul 2021 14:46:18 +0100 X-MC-Unique: c9JPzhnSOuerytt2WipVKQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.18; Sat, 17 Jul 2021 14:46:16 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.018; Sat, 17 Jul 2021 14:46:15 +0100 From: David Laight To: 'Eddie James' , "linux-spi@vger.kernel.org" CC: "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "robh+dt@kernel.org" , "broonie@kernel.org" , "openbmc@lists.ozlabs.org" , "joel@jms.id.au" Subject: RE: [PATCH 0/2] spi: fsi: Reduce max transfer size to 8 bytes Thread-Topic: [PATCH 0/2] spi: fsi: Reduce max transfer size to 8 bytes Thread-Index: AQHXekgD/1pxtg9xfUiNUvFFS56Yj6tHLOmA Date: Sat, 17 Jul 2021 13:46:15 +0000 Message-ID: <0ed7c393b7aa4252a48cd2397ac251eb@AcuMS.aculab.com> References: <20210716133915.14697-1-eajames@linux.ibm.com> In-Reply-To: <20210716133915.14697-1-eajames@linux.ibm.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eddie James > Sent: 16 July 2021 14:39 > > The security restrictions on the FSI-attached SPI controllers have > been applied universally to all controllers, so the controller can no > longer transfer more than 8 bytes for one transfer. Refactor the driver > to remove the looping and support for larger transfers, and remove the > "restricted" compatible string, as all the controllers are now > considered restricted. Aren't there significant performance (and device wear?) penalties for doing short SPI eeprom writes? IIRC (and I'm not getting my serial busses confused) a write request can request an aligned transfer of up to (typically) 32 bytes. At which point you need to wait for the status to indicate 'complete'. So restricting writes to 8 bytes increases block write times by a factor of 4. Increasing the numbers of writes by a factor or 4 may also have an effect on device wear - but that is more likely only affected by erase cycles. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)