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 X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0172EC433E0 for ; Mon, 1 Feb 2021 22:24:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA65364EBB for ; Mon, 1 Feb 2021 22:24:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229537AbhBAWYb (ORCPT ); Mon, 1 Feb 2021 17:24:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229524AbhBAWYa (ORCPT ); Mon, 1 Feb 2021 17:24:30 -0500 Received: from mail-pj1-x102f.google.com (mail-pj1-x102f.google.com [IPv6:2607:f8b0:4864:20::102f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CC441C06174A for ; Mon, 1 Feb 2021 14:23:49 -0800 (PST) Received: by mail-pj1-x102f.google.com with SMTP id g15so545414pjd.2 for ; Mon, 01 Feb 2021 14:23:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :mime-version; bh=bFIvq1iUBnF2uNTg/XXudUmq/LzMkpvkSS7sgQp5FVU=; b=DGUMvsvgtCsyOu5/4Ulasc7oslinB5t/JcszBUeqsrg01SmgO7CuSlAkMTB+IVPDpp +IMl/nxtXmJKqcIhqAuXke2BJIs0HW5Yg58xHGDP76qtLt4qwzAY1MRtIQHLT1+Aq5NR CV3XEEpjX5pMeXelmer6a1LbnGUxAaQdbTRN0p4wkVDvcm62X3B3VBkeA9U/4fwuiMI4 VXaJfjxQ0BUKSnQtejvqxOoV9J4EW5uG68o0W83kyDWnPe+dkNwgDX3kT9keZzcbAhPE TCIa13u2rHfK9e7QIsiEcep21m4J6m3rmoOHu1cjS9eRcMsh2adEd+ryF6V+ydIlwEGA UV9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:mime-version; bh=bFIvq1iUBnF2uNTg/XXudUmq/LzMkpvkSS7sgQp5FVU=; b=rUvzur69+ioHjpU4u63+vLwpJx2sl21hTT3+a326xZ1gFTzS1GusHqSqLK7ZrTAo8Z mFQMVna4j8l7LVF9sYh2skf7FxBaTflhrCkEBbLUkQNA8mc7gXU8gLf+x6uTQzLttIoz i4HPIj2TdOjF8rL84wqjlaWDHrekoI8y+BaBxpapxWrIEZSAKmRDCxLSKB2UoC18Bde6 G7r4zlcUPpVON7Ba+uPRvSCz/DfYmW4RSQEt8xrwyGVedn18jYkV9i06sXGsS1gfSefi nBnw/udhw3bsBOJNpleaAlaDfskJx8ukx0aIHvwrQUrVDEGiFo9CyJNdedD8/aoctRTL n67A== X-Gm-Message-State: AOAM531BbnTj31sS7uS6RmmghwmlEhEHHIJ4w3zERI4szTjs0wQW0Reh lgnnxVirdPOet+MMJV3eTPsjpw== X-Google-Smtp-Source: ABdhPJwMLSpGX0o+h2MFNvOFlmVc1GTAxnAxHJh9h3T5rMGwIj0rIL8nzRGWRD9t80SVGsT5UUpL2w== X-Received: by 2002:a17:902:bf44:b029:df:f0eb:cb33 with SMTP id u4-20020a170902bf44b02900dff0ebcb33mr19537849pls.13.1612218229062; Mon, 01 Feb 2021 14:23:49 -0800 (PST) Received: from [2620:15c:17:3:4a0f:cfff:fe51:6667] ([2620:15c:17:3:4a0f:cfff:fe51:6667]) by smtp.gmail.com with ESMTPSA id 123sm19531753pfd.91.2021.02.01.14.23.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Feb 2021 14:23:48 -0800 (PST) Date: Mon, 1 Feb 2021 14:23:47 -0800 (PST) From: David Rientjes To: Ben Widawsky cc: linux-cxl@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-pci@vger.kernel.org, Bjorn Helgaas , Chris Browy , Christoph Hellwig , Dan Williams , Ira Weiny , Jon Masters , Jonathan Cameron , Rafael Wysocki , Randy Dunlap , Vishal Verma , daniel.lll@alibaba-inc.com, "John Groves (jgroves)" , "Kelley, Sean V" Subject: Re: [PATCH 03/14] cxl/mem: Find device capabilities In-Reply-To: <20210201215857.ud5cpg7hbxj2j5bx@intel.com> Message-ID: References: <20210130002438.1872527-1-ben.widawsky@intel.com> <20210130002438.1872527-4-ben.widawsky@intel.com> <234711bf-c03f-9aca-e0b5-ca677add3ea@google.com> <20210201165352.wi7tzpnd4ymxlms4@intel.com> <32f33dd-97a-8b1c-d488-e5198a3d7748@google.com> <20210201215857.ud5cpg7hbxj2j5bx@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On Mon, 1 Feb 2021, Ben Widawsky wrote: > > > > > +static int cxl_mem_setup_mailbox(struct cxl_mem *cxlm) > > > > > +{ > > > > > + const int cap = cxl_read_mbox_reg32(cxlm, CXLDEV_MB_CAPS_OFFSET); > > > > > + > > > > > + cxlm->mbox.payload_size = > > > > > + 1 << CXL_GET_FIELD(cap, CXLDEV_MB_CAP_PAYLOAD_SIZE); > > > > > + > > > > > + /* 8.2.8.4.3 */ > > > > > + if (cxlm->mbox.payload_size < 256) { > > > > > + dev_err(&cxlm->pdev->dev, "Mailbox is too small (%zub)", > > > > > + cxlm->mbox.payload_size); > > > > > + return -ENXIO; > > > > > + } > > > > > > > > Any reason not to check cxlm->mbox.payload_size > (1 << 20) as well and > > > > return ENXIO if true? > > > > > > If some crazy vendor wanted to ship a mailbox larger than 1M, why should the > > > driver not allow it? > > > > > > > Because the spec disallows it :) > > I don't see it being the driver's responsibility to enforce spec correctness > though. In certain cases, I need to use the spec, like I have to pick /some/ > mailbox timeout. For other cases... > > I'm not too familiar with what other similar drivers may or may not do in > situations like this. The current 256 limit is mostly a reflection of that being > too small to even support advertised mandatory commands. So things can't work in > that scenario, but things can work if they have a larger register size (so long > as the BAR advertises enough space). > I don't think things can work above 1MB, either, though. Section 8.2.8.4.5 specifies 20 bits to define the payload length, if this is larger than cxlm->mbox.payload_size it would venture into the reserved bits of the command register. So is the idea to allow cxl_mem_setup_mailbox() to succeed with a payload size > 1MB and then only check 20 bits for the command register?