linux-kernel - Re: [PATCH] staging: vc04_services: tie up loose ends with dma_map

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Message-ID: <20161028154245.GA19454@kroah.com>
Date:   Fri, 28 Oct 2016 11:42:45 -0400
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Michael Zoran <mzoran@...wfest.net>
Cc:     devel@...verdev.osuosl.org, daniels@...labora.com,
        swarren@...dotorg.org, lee@...nel.org,
        linux-kernel@...r.kernel.org, eric@...olt.net, noralf@...nnes.org,
        linux-rpi-kernel@...ts.infradead.org, popcornmix@...il.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] staging: vc04_services: tie up loose ends with
 dma_map_sg conversion

On Fri, Oct 28, 2016 at 08:36:34AM -0700, Michael Zoran wrote:
> On Fri, 2016-10-28 at 11:31 -0400, Greg KH wrote:
> > On Fri, Oct 28, 2016 at 08:16:51AM -0700, Michael Zoran wrote:
> > > The conversion to dma_map_sg left a few loose ends.  This change
> > > ties up those loose ends.
> > > 
> > > 1. Settings the DMA mask is mandatory on 64 bit even though it
> > > is optional on 32 bit.  Set the mask so that DMA space is always
> > > in the lower 32 bit range of data on both platforms.
> > > 
> > > 2. The scatterlist was not completely initialized correctly.
> > > Initialize the list with sg_init_table so that DMA works correctly
> > > if scatterlist debugging is enabled in the build configuration.
> > > 
> > > 3. The error paths in create_pagelist were not consistent.  Make
> > > them all consistent by calling a helper function called
> > > cleanup_pagelistinfo to cleanup regardless of what state the
> > > pagelist
> > > is in.
> > > 
> > > 4. create_pagelist and free_pagelist had a very large amount of
> > > duplication in computing offsets into a single allocation of memory
> > > in the DMA area.  Introduce a new structure called the pagelistinfo
> > > that is appened to the end of the allocation to store necessary
> > > information to prevent duplication of code and make cleanup on
> > > errors
> > > easier.
> > > 
> > > When combined with a fix for vchiq_copy_from_user which is not
> > > included at this time, both functional and pings tests of
> > > vchiq_test
> > > now pass in both 32 bit and 64 bit modes.
> > > 
> > > Even though this cleanup could have been broken down to chunks,
> > > all the changes are to a single file and submitting it as a single
> > > related change should make reviewing the diff much easier then if
> > > it
> > > were submitted piecemeal.
> > 
> > No, it's harder.  A patch should only do one type of thing, this
> > patch
> > has to be reviewed thinking of 4 different things all at once, making
> > it
> > much more difficult to do so.
> > 
> > We write patches to be read easily, and make them easy to review.  We
> > don't write them in a way to be easy for the developer to create :)
> > 
> > Can you please break this up into a patch series?
> > 
> > thanks,
> > 
> > greg k-h
> 
> Point #1 and #2 would be very easy to seperate.   Point #3 and #4 are
> essentually a redo of two major functions and are where most of the
> changes are.
> 
> Would making #1 and #2 independent but combining #3 and #4 sufficient?

I don't know, try it and see what the patches look like.

Think about it from my point of view, which would be easier to review?

thanks,

greg k-h