linux-kernel - Re: [PATCH] dma-debug: Kconfig for PREALLOC_DMA_DEBUG_ENTRIES

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Date:   Mon, 3 Dec 2018 11:56:11 +0000
From:   John Garry <john.garry@...wei.com>
To:     Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>
CC:     Qian Cai <cai@....us>, <netdev@...r.kernel.org>,
        <linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux-foundation.org>, <yisen.zhuang@...wei.com>
Subject: Re: [PATCH] dma-debug: Kconfig for PREALLOC_DMA_DEBUG_ENTRIES

On 01/12/2018 16:36, Christoph Hellwig wrote:
> On Fri, Nov 30, 2018 at 07:39:50PM +0000, Robin Murphy wrote:
>> I was assuming the point was to also add something like
>>
>> 	default 131072 if HNS_ENET
>>
>> so that DMA debug doesn't require too much thought from the user. If they
>> still have to notice the overflow message and empirically figure out a
>> value that does work, rebuilding the kernel each time is far less
>> convenient than simply adding "dma_debug_entries=..." to their kernel
>> command line and rebooting, which they can do today. If they do already
>> know up-front that the default will need overriding and what the
>> appropriate value is, then the command line still seems seems just as
>> convenient.
>
> I'm not so fond of random drivers changing the defaults.  My idea
> was rather to have the config option so that the defconfig files for
> the Hisilicon SOCs with this hardware could select a larger number
> without making a total mess of the kernel configuration.
>
> If we really have to we could do different defaults, but I'd still
> much rather do this on a arch/platform basis than specific drivers.

As I understand, some drivers could even use much more than this 
(131072), to such a point where I can't imagine that we would want to 
set an arch default to support them. For this HNS_ENET case, it is arm64 
specific so it would be an arch defconfig.

Thanks,
John

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> iommu@...ts.linux-foundation.org
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>
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>

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