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[142.79.211.230]) by smtp.gmail.com with ESMTPSA id f9sm3160208otq.27.2021.05.17.06.48.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 May 2021 06:48:32 -0700 (PDT) Subject: Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled To: Jan Beulich Cc: Jann Horn , Lee Jones , Chunfeng Yun , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Greg Kroah-Hartman References: <8ccce25a-e3ca-cb30-f6a3-f9243a85a49b@suse.com> From: Connor Davis Message-ID: <16400ee4-4406-8b26-10c0-a423b2b1fed0@gmail.com> Date: Mon, 17 May 2021 07:48:52 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <8ccce25a-e3ca-cb30-f6a3-f9243a85a49b@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/17/21 3:32 AM, Jan Beulich wrote: > On 14.05.2021 02:56, Connor Davis wrote: >> Check if the debug capability is enabled in early_xdbc_parse_parameter, >> and if it is, return with an error. This avoids collisions with whatever >> enabled the DbC prior to linux starting. > Doesn't this go too far and prevent use even if firmware (perhaps > mistakenly) left it enabled? > > Jan Yes, but how is one supposed to distinguish the broken firmware and non-broken firmware cases? > >> Signed-off-by: Connor Davis >> --- >> drivers/usb/early/xhci-dbc.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c >> index be4ecbabdd58..ca67fddc2d36 100644 >> --- a/drivers/usb/early/xhci-dbc.c >> +++ b/drivers/usb/early/xhci-dbc.c >> @@ -642,6 +642,16 @@ int __init early_xdbc_parse_parameter(char *s) >> } >> xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset); >> >> + if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) { >> + pr_notice("xhci debug capability already in use\n"); >> + early_iounmap(xdbc.xhci_base, xdbc.xhci_length); >> + xdbc.xdbc_reg = NULL; >> + xdbc.xhci_base = NULL; >> + xdbc.xhci_length = 0; >> + >> + return -ENODEV; >> + } >> + >> return 0; >> } >> >> Thanks, Connor