linux-kernel - Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

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Date:   Wed, 7 Sep 2016 11:33:03 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Peter Chen <hzpeterchen@...il.com>, Arnd Bergmann <arnd@...db.de>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Stuart Yoder <stuart.yoder@....com>,
        Scott Wood <oss@...error.net>,
        David Fisher <david.fisher1@...opsys.com>,
        "Thang Q. Nguyen" <tqnguyen@....com>, Leo Li <pku.leo@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent
 dev

On 07/09/16 10:55, Peter Chen wrote:
[...]
>> Regarding the DMA configuration that you mention in ci_hdrc_add_device(),
>> I think we should replace 
>>
>>         pdev->dev.dma_mask = dev->dma_mask;
>>         pdev->dev.dma_parms = dev->dma_parms;
>>         dma_set_coherent_mask(&pdev->dev, dev->coherent_dma_mask);
>>
>> with of_dma_configure(), which has the chance to configure more than
>> just those three, as the dma API might look into different aspects:
>>
>> - iommu specific configuration
>> - cache coherency information
>> - bus type
>> - dma offset
>> - dma_map_ops pointer
>>
>> We try to handle everything in of_dma_configure() at configuration
>> time, and that would be the place to add anything else that we might
>> need in the future.
>>
> 
> Yes, I agree with you, but just like Felipe mentioned, we also need to
> consider PCI device, can we do something like gpiod_get_index does? Are
> there any similar APIs like of_dma_configure for ACPI?

Not yet, but Lorenzo has one in progress[1], primarily for the sake of
abstracting away the IOMMU configuration.

Robin.

[1]:http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1209911.html