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

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Date: Fri, 12 Apr 2024 17:34:34 +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>
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://github.com/DPDK/dpdk/blob/main/drivers/common/cnxk/roc_dpi.c

So this is a DPDK thing?  Ugh, do the networking people know about this?
If not, why aren't they reviewing this?

> > > +	__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 required.

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.

thanks,

greg k-h