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 Received: from ws5-mx01.kavi.com (ws5-mx01.kavi.com [34.193.7.191]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D96ABC4167B for ; Wed, 29 Nov 2023 08:35:25 +0000 (UTC) Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by ws5-mx01.kavi.com (Postfix) with ESMTP id 3145C1465CF for ; Wed, 29 Nov 2023 08:35:25 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 1A4A7986656 for ; Wed, 29 Nov 2023 08:35:25 +0000 (UTC) Received: from host09.ws5.connectedcommunity.org (host09.ws5.connectedcommunity.org [10.110.1.97]) by lists.oasis-open.org (Postfix) with QMQP id 0D3A39865EB; Wed, 29 Nov 2023 08:35:25 +0000 (UTC) Mailing-List: contact virtio-dev-help@lists.oasis-open.org; run by ezmlm List-ID: Sender: Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 1B441986642 for ; Wed, 29 Nov 2023 08:33:59 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: 9e2QBcQyMreptG27Yc9UVQ-1 From: Cornelia Huck To: Haixu Cui , Viresh Kumar Cc: virtio-dev@lists.oasis-open.org, virtio-comment@lists.oasis-open.org, harald.mommer@opensynergy.com, broonie@kernel.org, qiang4.zhang@linux.intel.com, quic_ztu@quicinc.com, alex.bennee@linaro.org, vincent.guittot@linaro.org In-Reply-To: <0674be8e-221f-479a-8da2-8a3e59e45bb9@quicinc.com> Organization: "Red Hat GmbH, Sitz: Werner-von-Siemens-Ring 12, D-85630 Grasbrunn, Handelsregister: Amtsgericht =?utf-8?Q?M=C3=BCnchen=2C?= HRB 153243, =?utf-8?Q?Gesch=C3=A4ftsf=C3=BChrer=3A?= Ryan Barnhart, Charles Cachera, Michael O'Neill, Amy Ross" References: <20231124072015.12655-1-quic_haixcui@quicinc.com> <20231127101750.6xmthho6lnppyw3k@vireshk-i7> <2ca987a6-eeb2-4ed6-9a12-10ae450eb4bf@quicinc.com> <20231129073022.ohxsfuawambvh3hm@vireshk-i7> <0674be8e-221f-479a-8da2-8a3e59e45bb9@quicinc.com> User-Agent: Notmuch/0.37 (https://notmuchmail.org) Date: Wed, 29 Nov 2023 09:33:49 +0100 Message-ID: <871qc9x8k2.fsf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Subject: [virtio-dev] Re: [virtio-comment] [PATCH] [PATCH v5] virtio-spi: add the device specification On Wed, Nov 29 2023, Haixu Cui wrote: > Hi Viresh, > > On 11/29/2023 3:30 PM, Viresh Kumar wrote: >> On 28-11-23, 20:58, Haixu Cui wrote: >>> On 11/27/2023 6:17 PM, Viresh Kumar wrote: >>>> On 24-11-23, 15:20, Haixu Cui wrote: >>>>> +For half-duplex read transfer, \field{rx_buf} is filled by Virtio SPI device and consumed >>>>> +by Virtio SPI driver. For half-duplex write transfer, \field{tx_buf} is filled by Virtio >>>>> +SPI driver and consumed by Virtio SPI device. And for full-duplex read and write transfer, >>>>> +both \field{tx_buf} and \field{rx_buf} are used. >>>> >>>> Should the length of both the buffers in full-duplex mode be same ? If yes, then >>>> this should be mentioned (in case it is not). >>>> >>> >>> No, there is no such limitation. Write and read buffers may be different is >>> size. >> >> Hmm, I worked with a SPI controller over a decade ago, and I must be forgetting >> something here I guess. But from whatever little I remember, with full-duplex >> transfer, data flows on both MOSI and MISO lines as soon as clock signal is >> applied. And so amount of data sent is always be equal to amount of data >> received by both sides. >> >> Also if I see Linux's implementation of the `struct spi_transfer` [1], I see >> `tx_buf`, `rx_buf` and a single `len` field, which applies to both the buffers. >> Which I guess is indicating that both buffers are supposed to be of same length. >> >> What am I missing ? > > Oh so sorry for that. And I don't make it clear. Yes, tx_buf and rx_buf > have the same size, Linux has such restriction. Just as you mention, > kernel level spi_transfer has single "len", the same for > spi_ioc_transfer passed from the userland. > > But I am not sure if this is in the scope of the spec. Because this is > ensured by Linux, but Virtio SPI driver won't also can't verify this. > This is a prerequisite for virtio spi processing requests. > > What is your suggestion? How about adding some descriptions here, like > "for full-duplex, tx_buf and rx_buf are same in size, this is guaranteed > by the kernel"? We must not really make any assumptions in the spec about concrete implementations (here, the Linux kernel), as someone implementing it in a different environment will need to make explicit choices. So, if tx_buf and rx_buf are required to be of the same size, it needs to be explicitly stated in the spec, or an implementation might choose to do it differently. --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org