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x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=gmail.com header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753713AbeCFPd4 (ORCPT ); Tue, 6 Mar 2018 10:33:56 -0500 Received: from mail-vk0-f50.google.com ([209.85.213.50]:36153 "EHLO mail-vk0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753559AbeCFPdz (ORCPT ); Tue, 6 Mar 2018 10:33:55 -0500 X-Google-Smtp-Source: AG47ELuVWcBhmz2rhMZvOGroWo2P6GRuAUm+isFsTmliK+Wm8lOVuU8u411W0/4+eZfeFj73e4NK1kAPQJ/WuRKmod0= MIME-Version: 1.0 In-Reply-To: <20180306142012.GB13586@sirena.org.uk> References: <20180303222716.26640-1-alexander.levin@microsoft.com> <20180303222716.26640-2-alexander.levin@microsoft.com> <20180305102310.GC8588@sirena.org.uk> <20180305200744.afw64js6wnmyfqrb@sasha-lappy> <20180305203533.GP8588@sirena.org.uk> <20180306142012.GB13586@sirena.org.uk> From: Jonas Gorski Date: Tue, 6 Mar 2018 16:33:34 +0100 Message-ID: Subject: Re: [PATCH AUTOSEL for 4.9 002/219] spi/bcm63xx: make spi subsystem aware of message size limits To: Mark Brown Cc: Sasha Levin , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 6 March 2018 at 15:20, Mark Brown wrote: > On Tue, Mar 06, 2018 at 02:42:43PM +0100, Jonas Gorski wrote: >> On 5 March 2018 at 21:35, Mark Brown wrote: > >> > It's exposing more capability information but it's in the "how did this >> > ever work without the fix" range, and I'd worry that this might cause us >> > to do something like start exercising handling code in client drivers >> > that had never been tested. Not that I can immediately see any client >> > drivers in mainline that actually pay attention... :/ > >> I would assume that most spi client drivers use short messages, so >> they aren't affected unless the max message size is really short. >> m25p80 on the other hand will do arbitrarily large transfers/reads, so >> there it was supported first. > > There's a bunch of SPI drivers that do firmware downloads which I'd > expect to be affected, the limit the device has is tiny so it's > relatively easy to bump into it. It's very rare for devices to be so > limited so unfortunately client drivers don't generally check though. Well, at least for bcm63xx it's very rare to have something other than a flash chip, a (broadcom) ethernet switch management interface, or a SLIC/SLAC attached to the SPI controller. And AFAICT of these three only the flash chip uses large SPI transfers. Furthermore, unless you have a development board, you won't be able to attach anything different to it. So the chance to bump into the limits with other drivers is rather low. I would assume that this is true for most systems with a limited SPI controller. I would hope that most board designers are sensible enough to not add devices that won't work ;-) Regards Jonas