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([2600:8803:e7e4:500:1cf0:fc72:ac61:29db]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-45f22e940c5sm3273917fac.18.2026.08.18.08.26.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Aug 2026 08:26:59 -0700 (PDT) Message-ID: <1c0fe275-3358-49ab-a238-7eb89127cce8@baylibre.com> Date: Tue, 18 Aug 2026 10:26:58 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/6] dt-bindings: iio: adc: ad7768-1: Document multidevice support To: =?UTF-8?Q?Nuno_S=C3=A1?= Cc: Jonathan Santos , linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org, michael.hennerich@analog.com, broonie@kernel.org, jonath4nns@gmail.com, marcelo.schmitt1@gmail.com, andriy.shevchenko@intel.com References: <9841fd2e-434f-48f3-90c1-d62718d6d4d2@baylibre.com> Content-Language: en-US From: David Lechner In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/18/26 10:14 AM, Nuno Sá wrote: > On Tue, Aug 18, 2026 at 10:02:50AM -0500, David Lechner wrote: >> On 8/17/26 6:32 PM, Jonathan Santos wrote: >>> The AD7768-1 family supports aggregating up to four devices on a single >>> SPI controller, with each device occupying a dedicated CS line and a >>> single data lane. >>> >>> Extend the `reg` property to accept up to 4 entries (one per device). >>> >>> Add `spi-rx-bus-width` property to declare the per-device lane count. >>> Since each lane is bound to one CS, the number of entries must match >>> `reg`. Make it required when `reg` has more than one entry. >>> >> I don't see why we should have to require the spi-rx-bus-width property. >> It seems logical that if it is not present, then we would assume one >> lane per CS. This is already how bindings work. >> >> For example, adi,ad4080 and ge,achc have multiple CS lines and don't >> require any bus width properties. > > Hmm that's my default then! I was the one requesting it. Basically > because of: > > https://elixir.bootlin.com/linux/v7.2/source/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml#L76 > > So I thought that $refing spi-peripheral-props.yaml and leaving the > default value would make dtbs_check to fail if one used > > spi-rx-bus-width = <1>, <1>, <1>, <1>; > > in DT. > > Won't it fail? > > And if we don't give the property I believe we'll have: > > https://elixir.bootlin.com/linux/v7.2/source/drivers/spi/spi.c#L2509 > > And given these series assumption of spi->num_rx_lanes == number of > devices (which I don't agree btw), I thought we would need to make > spi-rx-bus-width explicit in our bindings! I still think but I might be > wrong and I'm by no means an expert on dt bindings schemas work :) > > - Nuno Sá > >> Now that I'm reading the later patches again, it is jogging my memory. I forgot that we want this to operate like a single multi-lane device when reading data. So for that part, yes, having spi-rx-bus-width kind of makes sense. And I'm thinking that we might need a new property to indicate that this should be treated as a composite device rather than main + 3 auxiliary. I'll reply more about that in a later patch.