linux-kernel - Re: [RFC] ARM: bcm2835: register dmabounce on devices hooked to main interconnect

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Message-ID: <f15ef16e-8e5c-4e9b-1cb2-c6602b15a4ec@gmail.com>
Date:   Sat, 27 Jul 2019 10:36:46 +0200
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Christoph Hellwig <hch@....de>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Ray Jui <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Eric Anholt <eric@...olt.net>,
        Stefan Wahren <wahrenst@....net>, mbrugger@...e.com,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [RFC] ARM: bcm2835: register dmabounce on devices hooked to main
 interconnect



On 7/23/2019 6:34 PM, Christoph Hellwig wrote:
>> +static int bcm2835_needs_bounce(struct device *dev, dma_addr_t dma_addr, size_t size)
> 
> Too long line..
> 
>> +void __init bcm2835_init_early(void)
>> +{
>> +	if(of_machine_is_compatible("brcm,bcm2711"))
> 
> Odd formatting.
> 
> Otherwise this looks good to me.

Is this really the right way to solve this problem? First this is ARM
32-bit specific, and second, should not we have a way to indicate via
device tree that all peripherals behind the "soc" simple-bus parent node
are limited to 32-bit of DMA masks, but the specific memory map of the
BCM283x/BCM2711 makes it that only the last 1GB (0xC000_0000 -
0xffff_ffff) (which dma-ranges conveys already) is suitable for DMA into
the VPU uncached alias?
-- 
Florian