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

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Date:   Wed, 07 Sep 2016 13:47:22 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Robin Murphy <robin.murphy@....com>,
        Peter Chen <hzpeterchen@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     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\@vger.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\@lists.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


Hi,

Robin Murphy <robin.murphy@....com> writes:
> 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

not exported for drivers to use. If Lorenzo is trying to making a
matching API for ACPI systems, then it needs to follow what
of_dma_configure() is doing, and add an EXPORT_SYMBOL_GPL()

-- 
balbi

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