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=-6.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B08B2C5517A for ; Mon, 9 Nov 2020 06:41:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F5CD206C0 for ; Mon, 9 Nov 2020 06:41:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=broadcom.com header.i=@broadcom.com header.b="Pa0MsfJN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729542AbgKIGla (ORCPT ); Mon, 9 Nov 2020 01:41:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46252 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728904AbgKIGl3 (ORCPT ); Mon, 9 Nov 2020 01:41:29 -0500 Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7231BC0613D3 for ; Sun, 8 Nov 2020 22:41:29 -0800 (PST) Received: by mail-ed1-x536.google.com with SMTP id o20so7517395eds.3 for ; Sun, 08 Nov 2020 22:41:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=PW44boIOlxog7mR5V70et+LmFK6LuJaMUKuFmXxs7fc=; b=Pa0MsfJNDidS0QrctkgV4kpqKfCQ7fRL3s33R5C0JSaSTCRt9UOuE8uPvbZ9Jz+vJF eZbBDiztvYkmcuOxVmrcLZ8WC2HI6w87UfHaWXKufXacDXzeP86c+AEHDyFhpwWO4Gof Cyd+8RJeZ0vCcKBh+DKa1CB/+rnYUR2DYuu1Q= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PW44boIOlxog7mR5V70et+LmFK6LuJaMUKuFmXxs7fc=; b=PsdkDvLRCt/Bgpj2PEO7ELtlMLCKNl8pgP+YlwyNhGUdi3uDpMmtbGi5IDTzgj8Boj k54PL4d0kna+P2a3vyrpwbvsl3E7aaBUtLoHQlP+GUpgsSX4LwbMVmm4dIgTORS0iaNg Buekzsx/aMeYopfClZU29DVU9X/3T4/JVWn15SbK9AerNutb3OifI72pCd/QVIAMCQdi H9Cmz/Vo+aA4KsCyQYpmFcArahoNZWrsDmQm+jf9axDUvXAC1gVmeYwI1Blss6KTEkUp wv4YUS84O5JFF6TkxApJVEHIULyQY7c7B/TP4rPmTR8mqnDfnnFApI9+0BGcdkcBDvmG GpVw== X-Gm-Message-State: AOAM530vhaoKrb3z6hhDsmLTku7AI7bFhRcadSP+H9ItNEhnw4rixutU ijCP7N+aM55hYcNgSYMlLiWLmviMQ0sA+Gc1Ejnwwg== X-Google-Smtp-Source: ABdhPJy0nStOip0miCe8PSv3PPa21QRKI68Hu3+EsPlAG/kj8GU5PfM79f7PVnL5bLRGzpF447ExnWfDtD/yI9054z0= X-Received: by 2002:a05:6402:229a:: with SMTP id cw26mr13976124edb.271.1604904087108; Sun, 08 Nov 2020 22:41:27 -0800 (PST) MIME-Version: 1.0 References: <20201105060257.35269-1-vikas.gupta@broadcom.com> <20201105060257.35269-2-vikas.gupta@broadcom.com> <20201105000806.1df16656@x1.home> <20201105201208.5366d71e@x1.home> In-Reply-To: <20201105201208.5366d71e@x1.home> From: Vikas Gupta Date: Mon, 9 Nov 2020 12:11:15 +0530 Message-ID: Subject: Re: [RFC, v0 1/3] vfio/platform: add support for msi To: Alex Williamson Cc: Auger Eric , Cornelia Huck , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Vikram Prakash Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="0000000000000880b005b3a6da91" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --0000000000000880b005b3a6da91 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Alex, On Fri, Nov 6, 2020 at 8:42 AM Alex Williamson wrote: > > On Fri, 6 Nov 2020 08:24:26 +0530 > Vikas Gupta wrote: > > > Hi Alex, > > > > On Thu, Nov 5, 2020 at 12:38 PM Alex Williamson > > wrote: > > > > > > On Thu, 5 Nov 2020 11:32:55 +0530 > > > Vikas Gupta wrote: > > > > > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > > > > index 2f313a238a8f..aab051e8338d 100644 > > > > --- a/include/uapi/linux/vfio.h > > > > +++ b/include/uapi/linux/vfio.h > > > > @@ -203,6 +203,7 @@ struct vfio_device_info { > > > > #define VFIO_DEVICE_FLAGS_AP (1 << 5) /* vfio-ap device */ > > > > #define VFIO_DEVICE_FLAGS_FSL_MC (1 << 6) /* vfio-fsl-mc device= */ > > > > #define VFIO_DEVICE_FLAGS_CAPS (1 << 7) /* Info suppo= rts caps */ > > > > +#define VFIO_DEVICE_FLAGS_MSI (1 << 8) /* Device sup= ports msi */ > > > > __u32 num_regions; /* Max region index + 1 */ > > > > __u32 num_irqs; /* Max IRQ index + 1 */ > > > > __u32 cap_offset; /* Offset within info struct of first= cap */ > > > > > > This doesn't make any sense to me, MSIs are just edge triggered > > > interrupts to userspace, so why isn't this fully described via > > > VFIO_DEVICE_GET_IRQ_INFO? If we do need something new to describe it= , > > > this seems incomplete, which indexes are MSI (IRQ_INFO can describe > > > that)? We also already support MSI with vfio-pci, so a global flag f= or > > > the device advertising this still seems wrong. Thanks, > > > > > > Alex > > > > > Since VFIO platform uses indexes for IRQ numbers so I think MSI(s) > > cannot be described using indexes. > > That would be news for vfio-pci which has been describing MSIs with > sub-indexes within indexes since vfio started. > > > In the patch set there is no difference between MSI and normal > > interrupt for VFIO_DEVICE_GET_IRQ_INFO. > > Then what exactly is a global device flag indicating? Does it indicate > all IRQs are MSI? No, it's not indicating that all are MSI. The rationale behind adding the flag to tell user-space that platform device supports MSI as well. As you mentioned recently added capabilities can help on this, I`ll go through that. > > > The patch set adds MSI(s), say as an extension, to the normal > > interrupts and handled accordingly. > > So we have both "normal" IRQs and MSIs? How does the user know which > indexes are which? With this patch set, I think this is missing and user space cannot know that particular index is MSI interrupt. For platform devices there is no such mechanism, like index and sub-indexes to differentiate between legacy, MSI or MSIX as it=E2=80=99s th= ere in PCI. I believe for a particular IRQ index if the flag VFIO_IRQ_INFO_NORESIZE is used then user space can know which IRQ index has MSI(s). Does it make sense? Suggestions on this would be helpful. Thanks, Vikas > > > Do you see this is a violation? If > > Seems pretty unclear and dubious use of a global device flag. > > > yes, then we`ll think of other possible ways to support MSI for the > > platform devices. > > Macro VFIO_DEVICE_FLAGS_MSI can be changed to any other name if it > > collides with an already supported vfio-pci or if not necessary, we > > can remove this flag. > > If nothing else you're using a global flag to describe a platform > device specific augmentation. We've recently added capabilities on the > device info return that would be more appropriate for this, but > fundamentally I don't understand why the irq info isn't sufficient. > Thanks, > > Alex > --0000000000000880b005b3a6da91 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIIQPwYJKoZIhvcNAQcCoIIQMDCCECwCAQExDzANBglghkgBZQMEAgEFADALBgkqhkiG9w0BBwGg gg2UMIIE6DCCA9CgAwIBAgIOSBtqCRO9gCTKXSLwFPMwDQYJKoZIhvcNAQELBQAwTDEgMB4GA1UE CxMXR2xvYmFsU2lnbiBSb290IENBIC0gUjMxEzARBgNVBAoTCkdsb2JhbFNpZ24xEzARBgNVBAMT Ckdsb2JhbFNpZ24wHhcNMTYwNjE1MDAwMDAwWhcNMjQwNjE1MDAwMDAwWjBdMQswCQYDVQQGEwJC RTEZMBcGA1UEChMQR2xvYmFsU2lnbiBudi1zYTEzMDEGA1UEAxMqR2xvYmFsU2lnbiBQZXJzb25h bFNpZ24gMiBDQSAtIFNIQTI1NiAtIEczMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA tpZok2X9LAHsYqMNVL+Ly6RDkaKar7GD8rVtb9nw6tzPFnvXGeOEA4X5xh9wjx9sScVpGR5wkTg1 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