linux-kernel - Re: [PATCH 3/7] iommu: dart: Support >64 stream IDs

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Message-Id: <7ecde27b-05e9-4727-8441-e17916df237a@app.fastmail.com>
Date:   Thu, 05 Jan 2023 10:47:39 +0100
From:   "Sven Peter" <sven@...npeter.dev>
To:     "Hector Martin" <marcan@...can.st>,
        "Joerg Roedel" <joro@...tes.org>, "Will Deacon" <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>
Cc:     "Alyssa Rosenzweig" <alyssa@...enzweig.io>,
        "Janne Grunau" <j@...nau.net>, "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, iommu@...ts.linux.dev,
        asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] iommu: dart: Support >64 stream IDs

Hi,

On Thu, Jan 5, 2023, at 05:43, Hector Martin wrote:
> On 2023/01/04 22:37, Sven Peter wrote:
>>>  #include "dma-iommu.h"
>>>
>>> -#define DART_MAX_STREAMS 16
>>> +#define DART_MAX_STREAMS 256
>> 
>> Feels a bit wasteful to allocate 256-wide sid2group and save_{tcr,ttbr}
>> arrays even for the M1 where 16 are enough. But then again, that's still <100 KiB
>> for all DARTs combined and these machine have >8 GiB of RAM so it probably won't
>> make a difference
>
> Yeah, I don't think this is worth the extra fumbling around with dynamic
> allocation.
>
>>>  	/* enable all streams globally since TCR is used to control isolation */
>>> -	writel(DART_STREAM_ALL, dart->regs + DART_STREAMS_ENABLE);
>>> +	for (i = 0; i < BITS_TO_U32(dart->num_streams); i++)
>>> +		writel(U32_MAX, dart->regs + DART_STREAMS_ENABLE);
>> 
>> This seems weird: this code writes U32_MAX to the same register
>> again and again. 
>
> Whoops, that was supposed to have a `+ 4 * i` in there. Fixed for v2.

Great! Feel free to also add

Reviewed-by: Sven Peter <sven@...npeter.dev>

then.


Best,

Sven