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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CE49BCCA47F for ; Tue, 28 Jun 2022 13:03:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346068AbiF1NDl (ORCPT ); Tue, 28 Jun 2022 09:03:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56366 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346419AbiF1NDV (ORCPT ); Tue, 28 Jun 2022 09:03:21 -0400 Received: from loongson.cn (mail.loongson.cn [114.242.206.163]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3101C25C46 for ; Tue, 28 Jun 2022 06:03:19 -0700 (PDT) Received: from [10.20.42.19] (unknown [10.20.42.19]) by mail.loongson.cn (Coremail) with SMTP id AQAAf9Dx_08G_LpisKthAA--.7678S3; Tue, 28 Jun 2022 21:03:02 +0800 (CST) Subject: Re: [PATCH V14 4/7] PCI: loongson: Don't access non-existant devices To: Bjorn Helgaas , Huacai Chen Cc: Bjorn Helgaas , Lorenzo Pieralisi , Rob Herring , =?UTF-8?Q?Krzysztof_Wilczy=c5=84ski?= , linux-pci@vger.kernel.org, Xuefeng Li , Huacai Chen , Jiaxun Yang References: <20220627213847.GA1777956@bhelgaas> From: Jianmin Lv Message-ID: <4dbddb05-a0b4-047e-8784-c89279221f20@loongson.cn> Date: Tue, 28 Jun 2022 21:03:02 +0800 User-Agent: Mozilla/5.0 (X11; Linux loongarch64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20220627213847.GA1777956@bhelgaas> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-CM-TRANSID: AQAAf9Dx_08G_LpisKthAA--.7678S3 X-Coremail-Antispam: 1UD129KBjvJXoWxZw1xWr4UAr17Ary7tFyxXwb_yoWrAFy7pa y5Ja4SyF45tr12v3s2vF18W34aqFs3J3s5Jr4ay34q9r90yryFqrWDtFyYy347Jrs5WF1Y va9FqF1fGFWDAFJanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBa1xkIjI8I6I8E6xAIw20EY4v20xvaj40_Wr0E3s1l1IIY67AE w4v_Jr0_Jr4l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2 IY67AKxVW8JVW5JwA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwA2z4x0Y4vEx4A2 jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oVCq3wAS0I0E0xvYzxvE52 x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWUJVWU GwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4 x0x7Aq67IIx4CEVc8vx2IErcIFxwACI402YVCY1x02628vn2kIc2xKxwCYjI0SjxkI62AI 1cAE67vIY487MxkIecxEwVCm-wCF04k20xvY0x0EwIxGrwCF04k20xvE74AGY7Cv6cx26r yrJr1UJwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E 7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vIr41lIxAIcV C0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF 04k26cxKx2IYs7xG6rWUJVWrZr1UMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2js IEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x0JUdHUDUUUUU= X-CM-SenderInfo: 5oymxthqpl0qxorr0wxvrqhubq/ Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 2022/6/28 上午5:38, Bjorn Helgaas wrote: > On Fri, Jun 17, 2022 at 03:43:27PM +0800, Huacai Chen wrote: >> On LS2K/LS7A, some non-existant devices don't return 0xffffffff when >> scanning. This is a hardware flaw but we can only avoid it by software >> now. > > We should say what *does* happen if we do a config read to a device > that doesn't exit. Machine check, hang, etc? > The device is a hidden device(only for debug) that should not be scanned. If scanned in a non-normal way, the machine is hang(one case in ltp pci test can trigger the issue, which is explained blow). >> Signed-off-by: Huacai Chen >> --- >> drivers/pci/controller/pci-loongson.c | 19 +++++++++++++++++-- >> 1 file changed, 17 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c >> index a1222fc15454..e22142f75d97 100644 >> --- a/drivers/pci/controller/pci-loongson.c >> +++ b/drivers/pci/controller/pci-loongson.c >> @@ -134,10 +134,20 @@ static void __iomem *cfg0_map(struct loongson_pci *priv, int bus, >> return priv->cfg0_base + addroff; >> } >> >> +static bool pdev_is_existant(unsigned char bus, unsigned int device, unsigned int function) >> +{ >> + if ((bus == 0) && (device >= 9 && device <= 20) && (function > 0)) >> + return false; > > Why do you test pci_is_root_bus() below and "bus == 0" here? I think > you intend them both to test the same thing. If so, I think you > should test for "if (pci_is_root_bus(bus) ..." here. > I agree, I think we can only use pci_is_root_bus to do the work. > Generally speaking we only probe for functions > 0 if .0 is marked as > multi-function, so I guess this means 00:09.0 is marked as a > multi-function device, but config reads to 00:09.1 would fail? > Yes, definitely. Actually, the 00:09.0 is a single device, so fun1(09.1) will not be scanned(e.g. the fun1 will be not scanned on pci enumeration during kernel booting). But, there is one situation: when running ltp pci test case on LS7A, the 00:08.2 is a sata controller(a valid device), and the bus number(0) and devfn(0x42) are inputted to kernel api pci_scan_slot(), which has clear note: devfn must have zero function. So, apparently, the inputted devfn's function is not zero, but 2, and then in the pci_scan_slot(): for (fn = next_fn(bus, dev, 0); fn > 0; fn = next_fn(bus, dev, fn)) { dev = pci_scan_single_device(bus, devfn + fn); ... } 08.2,08.3...and 09.1 will be scanned one by one, so the 09.1(fun1) is scanned. >> + return true; > > Returning "true" here means "the device *may* exist," not "this device > *does* exist," right? If so, the function name probably should be > "pdev_may_exist()". > Yes, I think pdev_may_exist maybe better. > I guess that when we do a config read to a non-root bus device that > doesn't exist, e.g., "01:00.0", that read terminates with an > Unsupported Request error, the config read gets the ~0 data we expect? > Yes, I think so. >> +} >> + >> static void __iomem *pci_loongson_map_bus(struct pci_bus *bus, unsigned int devfn, >> int where) >> { >> unsigned char busnum = bus->number; >> + unsigned int device = PCI_SLOT(devfn); >> + unsigned int function = PCI_FUNC(devfn); >> struct loongson_pci *priv = pci_bus_to_loongson_pci(bus); >> >> if (pci_is_root_bus(bus)) >> @@ -147,8 +157,13 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus, unsigned int devf >> * Do not read more than one device on the bus other than >> * the host bus. >> */ >> - if (priv->data->flags & FLAG_DEV_FIX && >> - !pci_is_root_bus(bus) && PCI_SLOT(devfn) > 0) >> + if ((priv->data->flags & FLAG_DEV_FIX) && bus->self) { >> + if (!pci_is_root_bus(bus) && (device > 0)) >> + return NULL; >> + } >> + >> + /* Don't access non-existant devices */ >> + if (!pdev_is_existant(busnum, device, function)) >> return NULL; > > Is this a "forever" hardware bug that will never be fixed, or should > there be a flag like FLAG_DEV_FIX so we only do this on the broken > devices? > No, the next new version LS7A will correct it, so maybe we can use FLAG_DEV_FIX-like to address it. >> /* CFG0 can only access standard space */ >> -- >> 2.27.0 >>