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[192.26.37.52]) by smtp.gmail.com with ESMTPSA id x16sm25089864edr.52.2020.07.07.04.06.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Jul 2020 04:06:01 -0700 (PDT) From: Adrian Fiergolski X-Google-Original-From: Adrian Fiergolski Subject: Re: [PATCH v2 1/2] spi: Add the SPI daisy chain support. To: Mark Brown , Geert Uytterhoeven Cc: Lukas Wunner , kernel test robot , Rob Herring , linux-spi , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Linux Kernel Mailing List References: <202007040833.xIqR5rAw%lkp@intel.com> <20200706092247.20740-1-adrian.fiergolski@fastree3d.com> <20200706161810.GB6176@sirena.org.uk> <20200707102511.GE4870@sirena.org.uk> Message-ID: <2ed68c34-9b25-30a8-525b-aa469c9dd4d1@fastree3d.com> Date: Tue, 7 Jul 2020 13:06:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200707102511.GE4870@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07.07.2020 12:25, Mark Brown wrote: > On Mon, Jul 06, 2020 at 09:57:53PM +0200, Geert Uytterhoeven wrote: >> On Mon, Jul 6, 2020 at 6:18 PM Mark Brown wrote: >>> It would really help to have an example of how a client device will use >>> this, right now it's a bit hard to follow. Overall it feels like this >>> should be better abstracted, right now there's lots of ifdefs throughout >>> the code which make things unclear and also seem like they're going to >>> be fragile long term since realistically very few systems will be using >>> this. >> Can't the ifdefs be avoided by implementing this as a new SPI controller? >> I.e. the daisy chain driver will operate as a slave of the parent SPI >> controller, >> but will expose a new SPI bus to the daisy-chained slaves. > Yes, that might work. I do worry about locking issues with having a SPI > controller connected via SPI but we mostly only lock at the controller > level so it's probably fine. Not sure how this would perform either. I see your point here. I could evaluate how complicated it would be to abstract the spi-daisy_chain driver as an SPI controller for its nodes. Regards, Adrian