linux-kernel - Re: [PATCH v3 2/2] usb:dwc3: pass arch data to xhci-hcd child

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Date:	Mon, 4 Apr 2016 09:11:30 -0700
From:	santosh shilimkar <santosh.shilimkar@...cle.com>
To:	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	"Thang Q. Nguyen" <tqnguyen@....com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>,
	"Karicheri, Muralidharan" <m-karicheri2@...com>,
	Peter Ujfalusi <peter.ujfalusi@...com>, Phong Vo <pvo@....com>,
	Loc Ho <lho@....com>, patches <patches@....com>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	"Ben Dooks (embedded platforms)" <ben-linux@...ff.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH v3 2/2] usb:dwc3: pass arch data to xhci-hcd child

On 4/3/2016 11:28 PM, Felipe Balbi wrote:
> santosh shilimkar <santosh.shilimkar@...cle.com> writes:
>> +Arnd, RMK,
>>
>> On 4/1/2016 4:57 AM, Felipe Balbi wrote:
>>>
>>> Hi,
>>>
>>> Grygorii Strashko <grygorii.strashko@...com> writes:
>>>> On 04/01/2016 01:20 PM, Felipe Balbi wrote:
>>
>> [...]
>>
>>>> commit 7ace8fc8219e4cbbfd5b4790390d9a01a2541cdf
>>>> Author: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>>> Date:   Mon Jul 13 18:10:05 2015 +0900
>>>>
>>>>       usb: gadget: udc: core: Fix argument of dma_map_single for IOMMU
>>>>
>>>>       The dma_map_single and dma_unmap_single should set "gadget->dev.parent"
>>>>       instead of "&gadget->dev" in the first argument because the parent has
>>>>       a udc controller's device pointer.
>>>>       Otherwise, iommu functions are not called in ARM environment.
>>>>
>>>>       Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>>>       Signed-off-by: Felipe Balbi <balbi@...com>
>>>>
>>>> Above actually means that DMA configuration code can be dropped from
>>>> usb_add_gadget_udc_release() completely. Right?:
>>>
>>> true, but now I'm not sure what's better: copy all necessary bits from
>>> parent or just pass the parent device to all DMA API.
>>>
>>> Anybody to shed a light here ?
>>>
>> The expectation is drivers should pass the proper dev pointers and let
>> core DMA code deal with it since it knows the per device dma properties.
>
> okay, so how do you get proper DMA pointers with something like this:
>
> 	kdwc3_dma_mask = dma_get_mask(dev);
> 	dev->dma_mask = &kdwc3_dma_mask;
>
> This doesn't anything.
>
Drivers actually needs to touch dma_mask(s) only if the core DMA
code hasn't populated it it. I see Grygorii pointed out couple
of things already.

Reagrds,
Santosh