linux-kernel - Re: [PATCH v3 2/4] bus: fsl-mc: add restool userspace support

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Message-ID: <20180405165631.GB17495@lunn.ch>
Date:   Thu, 5 Apr 2018 18:56:31 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     gregkh <gregkh@...uxfoundation.org>
Cc:     Ruxandra Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Stuart Yoder <stuyoder@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Razvan Stefanescu <razvan.stefanescu@....com>,
        Roy Pledge <roy.pledge@....com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] bus: fsl-mc: add restool userspace support

> > Hi Andrew,
> > 
> > We're waiting for the DPIO driver (which we depend on) to be moved
> > out of staging first, it's currently under review:
> > https://lkml.org/lkml/2018/3/27/1086
> 
> That's stalled on my side right now as the merge window is open and I
> can't do any new stuff until after 4.17-rc1 is out.  So everyone please
> be patient a bit...

I took a quick look.

There are a few inline functions in .c files which is generally
frowned upon. Let the compiler decide.

e.g:

static inline struct dpaa2_io *service_select_by_cpu(struct dpaa2_io *d,	
                                                     int cpu)
static inline struct dpaa2_io *service_select(struct dpaa2_io *d)

dpaa2_io_down() seems to be too simple. dpaa2_io_create() sets up
interrupt triggers, notifications, and adds the new object to the
dpio_list. dpaa2_io_down() seems to just free the memory. Do
notifications need to be disabled, the object taken off the list?

dpaa2_io_store_create() allocates memory using kzalloc() and then uses
dma_map_single(,,DMA_FROM_DEVICE). The documentation says:

   DMA_FROM_DEVICE synchronisation must be done before the driver
   accesses data that may be changed by the device.  This memory
   should be treated as read-only by the driver.  If the driver needs
   to write to it at any point, it should be DMA_BIDIRECTIONAL (see
   below).

Since it has just been allocated, this seems questionable.

I'm also not sure where the correct call to
dma_map_single(,,DMA_FROM_DEVICE) is?  Should dpaa2_io_store_next()
doing this?

The DMA API usage might need a closer review.

    Andrew