From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Date: Sat, 15 Oct 2016 09:39:24 -0700 From: okaya@codeaurora.org To: Bharat Kumar Gogada Cc: Marc Zyngier , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Bjorn Helgaas , arnd@arndb.de, linux-pci-owner@vger.kernel.org Subject: Re: Why MSI is limited to 32 interrupts maximum In-Reply-To: <8520D5D51A55D047800579B0941471982594B127@XAP-PVEXMBX01.xlnx.xilinx.com> References: <8520D5D51A55D047800579B0941471982594B0F3@XAP-PVEXMBX01.xlnx.xilinx.com> <20161015141401.70d95035@why.wild-wind.fr.eu.org> <8520D5D51A55D047800579B0941471982594B127@XAP-PVEXMBX01.xlnx.xilinx.com> Message-ID: <304288d1efe5014b24d600be4438651a@codeaurora.org> List-ID: On 2016-10-15 06:30, Bharat Kumar Gogada wrote: >> On Sat, 15 Oct 2016 12:37:55 +0000 >> Bharat Kumar Gogada wrote: >> >> Hi Bharat, >> >> > Can anyone tell why MSI interrupts are limited to maximum 32 >> > interrupts, even though we have 16bit message data register ? >> >> That's the very definition of the original PCI MSI: Up to 32 >> consecutive interrupts >> per function, and a single doorbell address. >> MSI-X lifts that restriction and offers up to 2048 interrupts that do >> not have to >> be contiguous can target individual doorbells. Assuming your MSI >> controller >> advertises MSI-X support and that your devices do support it as well, >> you'll be >> able to enjoy those. >> > > Thanks Marc, so then only 5 bits of message data register will be > used, so what is the purpose rest of the bits ? > Data field is used to indicate which interrupt number is used. It does not need to start at 0. You have 32 consecutive interrupts starting from some arbitrary base. >> > >> > Regards, >> > Bharat >> > >> > >> > This email and any attachments are intended for the sole use of the >> > named recipient(s) and contain(s) confidential information that may be >> > proprietary, privileged or copyrighted under applicable law. If you >> > are not the intended recipient, do not read, copy, or forward this >> > email message or any attachments. Delete this email message and any >> > attachments immediately. >> > >> >> Please fix your email not to carry such disclaimer (or use a private >> email address >> if you can't work around your company policy). Posting confidential >> information >> on a public mailing list feels a bit silly. >> >> Thanks, >> >> M. >> -- >> Without deviation from the norm, progress is not possible. > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html