From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C7E5544C65C; Fri, 9 Oct 2026 06:36:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791527802; cv=none; b=GWbGc1OYqUUUGe+XPqXVTnM7/roCKQJ9OsrbvaUx76EBMrNNDGUSUaXm92iG1ZNba+sE3XpSAr7u7C7f53SOTXww2DE7nzAf/zJRbaAQzPkPIymE3TcZ7nMstPb8JVz3tAYIAU43vxVFOpu+yA3hn3Q2M879OKoUTJykoJ6Ke6s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791527802; c=relaxed/simple; bh=6a2jpBbdVOpf7H3trgEc/tTYPOnCEArKj8r/5oWzDvk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=W6VLwPoqiofhAB2ImTZXwykU3A/himRRGB5Di0mbQEAP84S63mThpJiGQXvzEznMVFt0AtT1OxagBVGfWDEKHos+2Txd7OoONLJ9zhTaqzLFuaR4lYKOswTDRWaNsVzwYON54E8YSK03oUJnaAkyDwxwkYEy9mFinAKZ8uJlX7g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V1XutQIp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="V1XutQIp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49A391F000FF; Fri, 9 Oct 2026 06:36:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791527800; bh=jx7npCcUuAQgxbfc2Agr3M33C2GZC5MXa2bHNjH9XTM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=V1XutQIpwwz5mwiG+zyoqyRx7m/dK2w1SNaRrVRJtlkY6r3AiFeSGSiykYCVe0ebY FuGrYGTsfUbrskqt3mmQz1oGnB9atvvwzruHWZb8BAFvTjhXbZLFIvQV+VNRMtl7FC gIQPi62qowHListw8Ht27F0wBc+Z2DAkoFuM5DQX5KNpnGhXVpnM6JfZWZxZJ4QOMM TFWhdFEtfoQdkFHE8auH52gS199INNOv3pqZPN+RjOJJtXq2m/BB9c7QgNHACDlVwn dB5v4TM0q+Blf4KWD7zOTXNFV1QGVlhKiCehkTPVSY8KNKDtDEPJnjljpta/9Uqtnz ZQn1eKEe5Ho0Q== Message-ID: Date: Fri, 9 Oct 2026 08:36:32 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/7] mailbox: goog-mba: Introduce the goog-mba mailbox driver To: Doug Anderson , Jassi Brar , Rob Herring , Saravana Kannan Cc: Joonwon Kang , Subhash Jadavani , Tudor Ambarus , Lucas Wei , Brian Norris , Peter Griffin , =?UTF-8?Q?Andr=C3=A9_Draszik?= , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" References: <20260714222338.2965707-1-dianders@chromium.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 28/09/2026 23:34, Doug Anderson wrote: > > ```C > static struct mbox_chan *goog_mba_fw_xlate(struct mbox_controller *mbox, > const struct fwnode_reference_args *sp) > { > int i; > > if (sp->nargs) > return ERR_PTR(-EINVAL); > > for (i = 0; i < mbox->num_chans; i++) { > if (!mbox->chans[i].cl) > return &mbox->chans[i]; > } > > return ERR_PTR(-EBUSY); > } > ``` > > Then the client loops around and requests the same channel over and > over again until it gets -EBUSY? Like: > > ```C > for (i = 0; i < FIFO_MAX; i++) { > client > chan[i] = mbox_request_channel(client[i], TX_CHAN); > if (IS_ERR(chan[i]) && PTR_ERR(chan[i]) == -EBUSY) > break; > } > fifo_depth = i; > ``` > > I _guess_ that works, but it still feels like a bit of a hack to me. > You said you were worried about people abusing the "has_queue" API. > The above feels like it's abusing the "fw_xlate" API, turning it from > something that is normally a "lookup" into an allocator function. > > +Rob, Saravana, and devicetree@vger.kernel.org. DT folks: is the above > something that looks right to you? There is no allocation in your xlate code above, so this is not that terrible as we talked on LPC. > > > I researched whether other upstream drivers use of_xlate() / > fw_xlate() as an "allocator" like this. I did find "exynos-mailbox," > which appears to be doing something similar. However, upon deeper > digging it seems like "exynos-mailbox" isn't using this dynamic > allocation for any compelling reason. It looks like, really, > "exynos-mailbox" should just be returning one channel. The client > (exynos-acpm) could just use the same channel for everything since: > * It actually gets the _real_ channel ID out of the data. > * It doesn't care about txdone. > * All it does is ring a doorbell and there's no queueing. > > > In any case, if using fw_xlate() as an allocator is truly the only way > to proceed, I'll finish my prototype and send a v2, but I'm still Why fw_xlate() would be an allocator? Can you extend your code to show that? I think doing any allocation in xlate() is calls is fundamentally wrong. These should not modify the state of the device, so no allocations, no device_link_add() etc. Why? There is simply no corresponding xlate_destroy() call. It's also confusing, because the meaning is to translate from one domain resource to another, not perform actual resource allocation. > skeptical that this is better than just adding queuing into the core. > Speaking of which, I actually want to go back to something you said > earlier. I asked a bit about this but I don't think I saw a response > (sorry if I missed it!): Best regards, Krzysztof