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[78.196.47.215]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42f89eac29dsm4271285e9.26.2024.10.04.12.14.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Oct 2024 12:14:41 -0700 (PDT) Date: Fri, 4 Oct 2024 21:14:39 +0200 From: Olivier Dautricourt To: =?utf-8?Q?Micha=C5=82?= Pecio Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, mathias.nyman@intel.com Subject: Re: [PATCH] usb: xhci: xhci_setup_port_arrays: early -ENODEV if maxports is 0. Message-ID: References: <20240930052336.80589-1-olivierdautricourt@gmail.com> <20241004125716.75c857ae@foxbook> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241004125716.75c857ae@foxbook> Hello, On Fri, Oct 04, 2024 at 12:57:16PM +0200, Michał Pecio wrote: > Hi, > > > If the controller reports HCSPARAMS1.maxports==0 then we can skip the > > whole function: it would fail later after doing a bunch of unnecessary > > stuff. It can occur on a buggy hardware (the value is driven by external > > signals). > > This function runs once during HC initialization, so what's the benefit > of bypassing it? Does it take unusually long time? Does it panic? > > It seems to alreday be written to handle such abnormal cases gracefully. That is correct, the case is handled without panic, but the 0 value gets silently propagated until it eventually fails on line 2220: if (xhci->usb2_rhub.num_ports == 0 && xhci->usb3_rhub.num_ports == 0) { xhci_warn(xhci, "No ports on the roothubs?\n"); return -ENODEV; } The benefits are only: - Reporting a more precise issue - Avoids iterating through the capability structures of the controller - failsafe if future changes This is totally a nitpick as the case is unusual, if you think it is not worth taking it upstream i'll understand. Kr, Olivier