Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Dragan Cvetic <draganc@xilinx.com>
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     "arnd@arndb.de" <arnd@arndb.de>, Michal Simek <michals@xilinx.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Derek Kiernan <dkiernan@xilinx.com>
Subject: RE: [PATCH V7 00/11] misc: xilinx sd-fec drive
Thread-Topic: [PATCH V7 00/11] misc: xilinx sd-fec drive
Thread-Index: AQHVIHtLLdGbOE767U2XbDHU36aibaamNrSAgAA5XPCAAM7egIARm4rg
Date:   Wed, 3 Jul 2019 11:04:22 +0000
Message-ID: <MN2PR02MB63682925A8D89F3B69001744CBFB0@MN2PR02MB6368.namprd02.prod.outlook.com>
References: <1560274185-264438-1-git-send-email-dragan.cvetic@xilinx.com>
 <20190621141553.GA16650@kroah.com>
 <CH2PR02MB635999D7374378CEA096FE72CBE70@CH2PR02MB6359.namprd02.prod.outlook.com>
 <20190622060135.GB26200@kroah.com>
In-Reply-To: <20190622060135.GB26200@kroah.com>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: xilinx.com does not designate
 permitted sender hosts)
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: bee70e3e-e6f8-440f-45f1-08d6ffa6340a
X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Jul 2019 11:04:22.0937
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 657af505-d5df-48d0-8300-c31994686c5c
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: draganc@xilinx.com
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR02MB5823
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> -----Original Message-----
> From: Greg KH [mailto:gregkh@linuxfoundation.org]
> Sent: Saturday 22 June 2019 07:02
> To: Dragan Cvetic <draganc@xilinx.com>
> Cc: arnd@arndb.de; Michal Simek <michals@xilinx.com>; linux-arm-kernel@li=
sts.infradead.org; robh+dt@kernel.org;
> mark.rutland@arm.com; devicetree@vger.kernel.org; linux-kernel@vger.kerne=
l.org; Derek Kiernan <dkiernan@xilinx.com>
> Subject: Re: [PATCH V7 00/11] misc: xilinx sd-fec drive
>=20
> On Fri, Jun 21, 2019 at 05:49:45PM +0000, Dragan Cvetic wrote:
> >
> >
> > > -----Original Message-----
> > > From: Greg KH [mailto:gregkh@linuxfoundation.org]
> > > Sent: Friday 21 June 2019 15:16
> > > To: Dragan Cvetic <draganc@xilinx.com>
> > > Cc: arnd@arndb.de; Michal Simek <michals@xilinx.com>; linux-arm-kerne=
l@lists.infradead.org; robh+dt@kernel.org;
> > > mark.rutland@arm.com; devicetree@vger.kernel.org; linux-kernel@vger.k=
ernel.org; Derek Kiernan <dkiernan@xilinx.com>
> > > Subject: Re: [PATCH V7 00/11] misc: xilinx sd-fec drive
> > >
> > > On Tue, Jun 11, 2019 at 06:29:34PM +0100, Dragan Cvetic wrote:
> > > > This patchset is adding the full Soft Decision Forward Error
> > > > Correction (SD-FEC) driver implementation, driver DT binding and
> > > > driver documentation.
> > > >
> > > > Forward Error Correction (FEC) codes such as Low Density Parity
> > > > Check (LDPC) and turbo codes provide a means to control errors in
> > > > data transmissions over unreliable or noisy communication
> > > > channels. The SD-FEC Integrated Block is an optimized block for
> > > > soft-decision decoding of these codes. Fixed turbo codes are
> > > > supported directly, whereas custom and standardized LDPC codes
> > > > are supported through the ability to specify the parity check
> > > > matrix through an AXI4-Lite bus or using the optional programmable
> > > > (PL)-based support logic. For the further information see
> > > > https://www.xilinx.com/support/documentation/ip_documentation/
> > > > sd_fec/v1_1/pg256-sdfec-integrated-block.pdf
> > > >
> > > > This driver is a platform device driver which supports SDFEC16
> > > > (16nm) IP. SD-FEC driver supports LDPC decoding and encoding and
> > > > Turbo code decoding. LDPC codes can be specified on
> > > > a codeword-by-codeword basis, also a custom LDPC code can be used.
> > > >
> > > > The SD-FEC driver exposes a char device interface and supports
> > > > file operations: open(), close(), poll() and ioctl(). The driver
> > > > allows only one usage of the device, open() limits the number of
> > > > driver instances. The driver also utilize Common Clock Framework
> > > > (CCF).
> > > >
> > > > The control and monitoring is supported over ioctl system call.
> > > > The features supported by ioctl():
> > > > - enable or disable data pipes to/from device
> > > > - configure the FEC algorithm parameters
> > > > - set the order of data
> > > > - provide a control of a SDFEC bypass option
> > > > - activates/deactivates SD-FEC
> > > > - collect and provide statistical data
> > > > - enable/disable interrupt mode
> > >
> > > Is there any userspace tool that talks to this device using these cus=
tom
> > > ioctls yet?
> > >
> > Tools no, but could be the customer who is using the driver.
>=20
> I don't understand this.  Who has written code to talk to these
> special ioctls from userspace?  Is there a pointer to that code
> anywhere?
>=20
> > > Doing a one-off ioctl api is always a risky thing, you are pretty muc=
h
> > > just creating brand new system calls for one piece of hardware.
> > >
> >
> > Why is that wrong and what is the risk?
>=20
> You now have custom syscalls for one specfic piece of hardware that you
> now have to maintain working properly for the next 40+ years.  You have
> to make sure those calls are correct and that this is the correct api to
> talk to this hardware.
>=20


The only idea I have got from the comments are to do more abstraction
eg. have a few ioctls with the abstraction done through the passing argumen=
ts?


> > What would you propose?
> > Definitely, I have to read about this.
>=20
> What is this hardware and what is it used for?  Who will be talking to
> it from userspace?  What userspace workload uses it?  What tools need to
> talk to it?  Where is the code that uses these new apis?
>=20
> thanks,
>=20
> greg k-h