From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:51200) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gqk7h-00087f-Fz for qemu-devel@nongnu.org; Mon, 04 Feb 2019 14:41:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gqjw4-00018R-Kd for qemu-devel@nongnu.org; Mon, 04 Feb 2019 14:29:44 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:54528 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gqjvr-0000oP-7X for qemu-devel@nongnu.org; Mon, 04 Feb 2019 14:29:31 -0500 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x14JOd9s013466 for ; Mon, 4 Feb 2019 14:29:24 -0500 Received: from e34.co.us.ibm.com (e34.co.us.ibm.com [32.97.110.152]) by mx0a-001b2d01.pphosted.com with ESMTP id 2qercrh8hk-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 04 Feb 2019 14:29:24 -0500 Received: from localhost by e34.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 4 Feb 2019 19:29:23 -0000 References: <1548768562-20007-1-git-send-email-jjherne@linux.ibm.com> <1548768562-20007-11-git-send-email-jjherne@linux.ibm.com> <735ca9ff-76e3-966f-6fbc-a72bf994b413@linux.ibm.com> <20190204121319.32915fd6.cohuck@redhat.com> From: Farhan Ali Date: Mon, 4 Feb 2019 14:29:18 -0500 MIME-Version: 1.0 In-Reply-To: <20190204121319.32915fd6.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Subject: Re: [Qemu-devel] [PATCH 10/15] s390-bios: Support for running format-0/1 channel programs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cornelia Huck Cc: "Jason J. Herne" , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com On 02/04/2019 06:13 AM, Cornelia Huck wrote: > On Thu, 31 Jan 2019 12:31:00 -0500 > Farhan Ali wrote: > >> On 01/29/2019 08:29 AM, Jason J. Herne wrote: >>> Add struct for format-0 ccws. Support executing format-0 channel >>> programs and waiting for their completion before continuing execution. >>> This will be used for real dasd ipl. >>> >>> Add cu_type() to channel io library. This will be used to query control >>> unit type which is used to determine if we are booting a virtio device or a >>> real dasd device. >>> >>> Signed-off-by: Jason J. Herne >>> --- >>> pc-bios/s390-ccw/cio.c | 114 +++++++++++++++++++++++++++++++++++++++ >>> pc-bios/s390-ccw/cio.h | 127 ++++++++++++++++++++++++++++++++++++++++++-- >>> pc-bios/s390-ccw/s390-ccw.h | 1 + >>> pc-bios/s390-ccw/start.S | 33 +++++++++++- >>> 4 files changed, 270 insertions(+), 5 deletions(-) > >>> +/* >>> + * Executes a channel program at a given subchannel. The request to run the >>> + * channel program is sent to the subchannel, we then wait for the interrupt >>> + * signaling completion of the I/O operation(s) performed by the channel >>> + * program. Lastly we verify that the i/o operation completed without error and >>> + * that the interrupt we received was for the subchannel used to run the >>> + * channel program. >>> + * >>> + * Note: This function assumes it is running in an environment where no other >>> + * cpus are generating or receiving I/O interrupts. So either run it in a >>> + * single-cpu environment or make sure all other cpus are not doing I/O and >>> + * have I/O interrupts masked off. >>> + */ >>> +int do_cio(SubChannelId schid, uint32_t ccw_addr, int fmt) >>> +{ >>> + CmdOrb orb = {}; >>> + Irb irb = {}; >>> + sense_data_eckd_dasd sd; >>> + int rc, retries = 0; >>> + >>> + IPL_assert(fmt == 0 || fmt == 1, "Invalid ccw format"); >>> + >>> + /* ccw_addr must be <= 24 bits and point to at least one whole ccw. */ >>> + if (fmt == 0) { >>> + IPL_assert(ccw_addr <= 0xFFFFFF - 8, "Invalid ccw address"); >>> + } >>> + >>> + orb.fmt = fmt ; >>> + orb.pfch = 1; /* QEMU's cio implementation requires prefetch */ >>> + orb.c64 = 1; /* QEMU's cio implementation requires 64-bit idaws */ >>> + orb.lpm = 0xFF; /* All paths allowed */ >>> + orb.cpa = ccw_addr; >>> + >>> + while (true) { >>> + rc = ssch(schid, &orb); >>> + if (rc == 1) { >>> + /* Status pending, not sure why. Let's eat the status and retry. */ >>> + tsch(schid, &irb); >>> + retries++; >>> + continue; >>> + } >>> + if (rc) { >>> + print_int("ssch failed with rc=", rc); >>> + break; >>> + } >>> + >>> + consume_io_int(); >>> + >>> + /* collect status */ >>> + rc = tsch(schid, &irb); >>> + if (rc) { >>> + print_int("tsch failed with rc=", rc); >>> + break; >>> + } >>> + >>> + if (!irb_error(&irb)) { >>> + break; >>> + } >>> + >>> + /* >>> + * Unexpected unit check, or interface-control-check. Use sense to >>> + * clear unit check then retry. >>> + */ >>> + if ((unit_check(&irb) || iface_ctrl_check(&irb)) && retries <= 2) { >>> + basic_sense(schid, &sd, sizeof(sd)); >> >> We are using basic sense to clear any unit check or ifcc, but is it >> possible for the basic sense to cause another unit check? >> >> The chapter on Basic Sense in the Common I/O Device Commands >> (http://publibz.boulder.ibm.com/support/libraryserver/FRAMESET/dz9ar501/2.1?SHELF=&DT=19920409154647&CASE=) >> says this: >> >> "" >> The basic sense command initiates a sense operation at all devices >> and cannot cause the command-reject, intervention-required, >> data-check, or overrun bit to be set to one. If the control unit >> detects an equipment malfunction or invalid checking-block code >> (CBC) on the sense-command code, the equipment-check or bus-out-check >> bit is set to one, and unit check is indicated in the device-status >> byte. >> "" >> >> If my understanding is correct, if there is an equipment malfunction >> then the control unit can return a unit check even for a basic sense. >> This can lead to infinite recursion in the bios. > > I think the retries variable is supposed to take care of that. > If I understand the code correctly, the retries variable cannot prevent infinite recursion. Because every time we get a unit check we do a basic sense which calls the do_cio function again. If that basic sense returns a unit check we do another basic sense.... > What I don't understand is why we do the basic sense after an IFCC? > Wouldn't it make more sense to simply retry the original command in > that case? > >> >> >> >>> + retries++; >>> + continue; >>> + } >>> + >>> + break; >>> + } >>> + >>> + return rc; >>> +} >> > >