linux-kernel - Re: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add Octeon CN10K DPI administrative driver

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Message-ID: <2024041351-endowment-underrate-4b8d@gregkh>
Date: Sat, 13 Apr 2024 07:47:36 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Vamsi Krishna Attunuru <vattunuru@...vell.com>
Cc: "arnd@...db.de" <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jerin Jacob <jerinj@...vell.com>
Subject: Re: [EXTERNAL] Re: [PATCH v5 1/1] misc: mrvl-cn10k-dpi: add Octeon
 CN10K DPI administrative driver

On Fri, Apr 12, 2024 at 04:19:58PM +0000, Vamsi Krishna Attunuru wrote:
> 
> 
> > -----Original Message-----
> > From: Greg KH <gregkh@...uxfoundation.org>
> > Sent: Friday, April 12, 2024 9:05 PM
> > To: Vamsi Krishna Attunuru <vattunuru@...vell.com>
> > Cc: arnd@...db.de; linux-kernel@...r.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 wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Greg KH <gregkh@...uxfoundation.org>
> > > > Sent: Friday, April 12, 2024 5:57 PM
> > > > To: Vamsi Krishna Attunuru <vattunuru@...vell.com>
> > > > Cc: arnd@...db.de; linux-kernel@...r.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 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=https-
> > 3A__github.com_DPDK_d
> > > pdk_blob_main_drivers_common_cnxk_roc-
> > 5Fdpi.c&d=DwIBAg&c=nKjWec2b6R0mO
> > >
> > yPaz7xtfQ&r=WllrYaumVkxaWjgKto6E_rtDQshhIhik2jkvzFyRhW8&m=o3EhoL
> > s7dsod
> > > -YHS438Wl2Pf_MKMBYegGSKteoX3qFTB0HV897ykpCVbTp-
> > nmj4e&s=A6TJDFUtPm3ksJh
> > > qop89CL8GgKj4sjkJIVi1-RdnUr8&e=
> > 
> > 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 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 resources.

So this is something that the PCI core should be concerned about then?

> 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/administrative function
> driver running in the kernel.

Are there other devices/drivers that do this today in Linux?  Why make a
device-specific api for this common functionality?

thanks,

greg k-h