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From: Vamsi Krishna Attunuru <vattunuru@marvell.com>
To: Greg KH <gregkh@linuxfoundation.org>
CC: "arnd@arndb.de" <arnd@arndb.de>,
        "linux-kernel@vger.kernel.org"
	<linux-kernel@vger.kernel.org>,
        Jerin Jacob <jerinj@marvell.com>
Subject: RE: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add Octeon
 CN10K DPI administrative driver
Thread-Topic: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add Octeon
 CN10K DPI administrative driver
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Date: Sat, 13 Apr 2024 10:58:37 +0000
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> -----Original Message-----
> From: Greg KH <gregkh@linuxfoundation.org>
> Sent: Saturday, April 13, 2024 11:18 AM
> To: Vamsi Krishna Attunuru <vattunuru@marvell.com>
> Cc: arnd@arndb.de; linux-kernel@vger.kernel.org; Jerin Jacob
> <jerinj@marvell.com>
> Subject: Re: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add
> Octeon CN10K DPI administrative driver
>=20
> On Fri, Apr 12, 2024 at 04:19:58PM +0000, Vamsi Krishna Attunuru wrote:
> >
> >
> > > -----Original Message-----
> > > From: Greg KH <gregkh@linuxfoundation.org>
> > > Sent: Friday, April 12, 2024 9:05 PM
> > > To: Vamsi Krishna Attunuru <vattunuru@marvell.com>
> > > Cc: arnd@arndb.de; linux-kernel@vger.kernel.org
> > > Subject: Re: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add
> > > Octeon CN10K DPI administrative driver
> > >
> > > On Fri, Apr 12, 2024 at 01:56:36PM +0000, Vamsi Krishna Attunuru wrot=
e:
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Greg KH <gregkh@linuxfoundation.org>
> > > > > Sent: Friday, April 12, 2024 5:57 PM
> > > > > To: Vamsi Krishna Attunuru <vattunuru@marvell.com>
> > > > > Cc: arnd@arndb.de; linux-kernel@vger.kernel.org
> > > > > Subject: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add
> > > > > Octeon CN10K DPI administrative driver
> > > > >
> > > > > Prioritize security for external emails: Confirm sender and
> > > > > content safety before clicking links or opening attachments
> > > > >
> > > > > ----------------------------------------------------------------
> > > > > ----
> > > > > -- On Fri, Apr 12, 2024 at 05:10:05AM -0700, Vamsi Attunuru wrote=
:
> > > > > > Adds a misc driver for Marvell CN10K DPI(DMA Engine) device's
> > > > > > physical function which initializes DPI DMA hardware's global
> > > > > > configuration and enables hardware mailbox channels between
> > > > > > physical function (PF) and it's virtual functions (VF). VF
> > > > > > device drivers (User space drivers) use this hw mailbox to
> > > > > > communicate any required device configuration on it's respectiv=
e
> VF device.
> > > > > > Accordingly, this DPI PF driver provisions the VF device resour=
ces.
> > > > > >
> > > > > > At the hardware level, the DPI physical function (PF) acts as
> > > > > > a management interface to setup the VF device resources, VF
> > > > > > devices are only provisioned to handle or control the actual
> > > > > > DMA Engine's data transfer
> > > > > capabilities.
> > > > >
> > > > > No pointer to the userspace code that uses this?  Why not?  How
> > > > > are we supposed to be able to review this?
> > > >
> > > > Userspace code will use two functionalities (mailbox & ioctl) from
> > > > this driver. DPDK DMA driver uses the mailbox and the dpdk
> > > > application uses the ioctl to setup the device attributes. We are
> > > > waiting for this kernel driver get merged  to update the
> > > > corresponding support in DPDK
> > > driver and applications. I will provide the pointers to both the use
> > > cases in userspace code.
> > > > Meanwhile below is the current dpdk dma driver that uses sysfs
> > > > based scheme to convey mbox requests to the kernel DPI driver
> > > > which gets
> > > replaced with hardware mailbox scheme once mrvl-cn10k-dpi kernel
> > > driver is merged.
> > > > https://urldefense.proofpoint.com/v2/url?u=3Dhttps-
> > > 3A__github.com_DPDK_d
> > > > pdk_blob_main_drivers_common_cnxk_roc-
> > > 5Fdpi.c&d=3DDwIBAg&c=3DnKjWec2b6R0mO
> > > >
> > >
> yPaz7xtfQ&r=3DWllrYaumVkxaWjgKto6E_rtDQshhIhik2jkvzFyRhW8&m=3Do3EhoL
> > > s7dsod
> > > > -YHS438Wl2Pf_MKMBYegGSKteoX3qFTB0HV897ykpCVbTp-
> > > nmj4e&s=3DA6TJDFUtPm3ksJh
> > > > qop89CL8GgKj4sjkJIVi1-RdnUr8&e=3D
> > >
> > > So this is a DPDK thing?  Ugh, do the networking people know about th=
is?
> > > If not, why aren't they reviewing this?
> >
> > Actually, It's not networking related. Like the Linux kernel, DPDK
> > also supports multiple subsystems like network, scheduler, DMA,
> > mempool etc. Regarding the usecases, the DPDK Marvell DMA/DPI VF
> > driver interacts(over hardware mailbox) with the mrvl-cn10k-dpi misc
> kernel driver(administrative driver) for setting up the VF device resourc=
es.
>=20
> So this is something that the PCI core should be concerned about then?

No, it's a normal PCIe sriov capability implemented in all sriov capable PC=
Ie devices.
Our PF device aka this driver in kernel space service mailbox requests from=
 userspace
applications via VF devices. For instance, DPI VF device from user space wr=
ites into
mailbox registers and the DPI hardware triggers an interrupt to DPI PF devi=
ce.
Upon PF interrupt, this driver services the mailbox requests.

>=20
> > DPDK is one example that uses this driver, there can be other
> > userspace generic frameworks/applications where the virtual functions
> > are binded to userspace drivers and interact with physical/administrati=
ve
> function driver running in the kernel.
>=20
> Are there other devices/drivers that do this today in Linux?  Why make a
> device-specific api for this common functionality?

The apis defined in this driver are specific to Marvell DPI hardware. For i=
nstance,
the variables molr(max outstanding load requests), fifo_max, ebus_port are
DPI hardware specific. Generally, drivers use driver-specific api to config=
ure
any device-specific configuration which does not fit in common functionalit=
y right.

Mailbox operations like dpi_queue_open & close are requests sent from VF de=
vice
to PF device for setting up the VF queue resources.

>=20
> thanks,
>=20
> greg k-h