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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
Thread-Index: AQHajNJlUzRgj48oqke7eNtbl1jogrFkj7+AgAAOmwCAACXXAIAAAZzA
Date: Fri, 12 Apr 2024 16:19:58 +0000
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> -----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
>=20
> On Fri, Apr 12, 2024 at 01:56:36PM +0000, Vamsi Krishna Attunuru wrote:
> >
> >
> > > -----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 respective VF device.
> > > > Accordingly, this DPI PF driver provisions the VF device resources.
> > > >
> > > > 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 case=
s 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 i=
s
> 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
>=20
> So this is a DPDK thing?  Ugh, do the networking people know about this?
> If not, why aren't they reviewing this?

Actually, It's not networking related. Like the Linux kernel, DPDK also sup=
ports multiple subsystems like
network, scheduler, DMA, mempool etc. Regarding the usecases, the DPDK Marv=
ell DMA/DPI VF driver
interacts(over hardware mailbox) with the mrvl-cn10k-dpi misc kernel driver=
(administrative driver) for setting
up the VF device resources.

DPDK is one example that uses this driver, there can be other userspace gen=
eric frameworks/applications
where the virtual functions are binded to userspace drivers and interact wi=
th physical/administrative function
driver running in the kernel.

>=20
> > > > +	__u64 update_molr; /* '1' to update engine MOLR */
> > >
> > > You "burn" a whole 64 for 1 bit?  That feels wrong, who on your end
> > > reviewed this api to be correct?
> >
> > Just for the explicit alignment, defined all variables as __u64. I
> > will shrink it to minimal sizes considering any reserved fields if requ=
ired.
>=20
> The alignment is fine, but wasting 63 bits feels odd, make it a bit field=
 at worst
> case, or just make it __u8 if you don't want a bitfield.

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