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[2001:1c00:c14:2800:ec23:a060:24d5:2453]) by smtp.gmail.com with ESMTPSA id i5sm1778299edv.29.2019.10.05.03.47.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Oct 2019 03:47:17 -0700 (PDT) To: Thomas Gleixner , Linux Kernel Mailing List From: Hans de Goede Subject: Is IRQ number 0 a valid IRQ ? Cc: Greg Kroah-Hartman Message-ID: <4ef7a462-5ded-0ac7-242e-888a9d36362b@redhat.com> Date: Sat, 5 Oct 2019 12:47:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 Content-Language: en-US X-MC-Unique: K9onPquIN_64jjlteFICCA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Thomas, This is something which I have been wondering for ever since there are several places in the kernel where IRQ number 0 is treated as not being valid (as no IRQ found mostly I guess). Where as other places do treat IRQ number 0 as valid... ? Some examples which treat IRQ 0 special: drivers/base/platform.c: __platform_get_irq() : if (IS_ENABLED(CONFIG_OF_IRQ) && dev->dev.of_node) { int ret; ret =3D of_irq_get(dev->dev.of_node, num); if (ret > 0 || ret =3D=3D -EPROBE_DEFER) return ret; } Note if (ret > 0) not if (ret >=3D 0) Other example: drivers/usb/dwc3/gadget.c: dwc3_gadget_get_irq() : if (!irq) irq =3D -EINVAL; So 2 questions: 1) Is this special handling of IRQ number 0 valid code, or just mostly some leftover from older days when IRQ number 0 was maybe special ? 2) Either way (*) I think we (I volunteer) should document this somewhere, other then adding a note about this to the platform_get_irq docs any other place where it would be good to specify this? Regards, Hans *) Either IRQ number 0 is not special and then we need to stop the cargo-culting of treating it special, or it is special and then we need to document that.