Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 28 Jun 2023 12:02:47 +0100
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Li Chen <me@linux.beauty>
Cc:     dmaengine <dmaengine@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: Should dma_map_single take the dma controller or its consumer as
 an argument?
Message-ID: <ZJwTV59xRlUBit+N@shell.armlinux.org.uk>
References: <18901a6cbf0.c9e3e099688173.4166132371304083225@linux.beauty>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <18901a6cbf0.c9e3e099688173.4166132371304083225@linux.beauty>
Sender: Russell King (Oracle) <linux@armlinux.org.uk>
Precedence: bulk

On Wed, Jun 28, 2023 at 06:57:35PM +0800, Li Chen wrote:
> Hi all,
> 
> I recently encountered an issue where the dma_mask was set in the DMA controller's driver, but the consumer peripheral driver didn't set its own dma_mask.

It should always take the device that is *actually* performing the DMA,
since that is the device that has restrictions on what addresses can be
accessed, etc.

Devices that "consume" the data from a DMA controller don't access
memory - they are merely the targets, and they can't on their own access
host memory. Therefore, their dma mask _should_ be irrelevant.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!