linux-kernel - Re: [PATCH] usb: chipidea: Configure DMA properties and ops from DT

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Date:	Wed, 2 Mar 2016 16:59:33 -0600
From:	Li Yang <leoli@...escale.com>
To:	Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, Peter Chen <Peter.Chen@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Rajesh Bhagat <rajesh.bhagat@....com>
Subject: Re: [PATCH] usb: chipidea: Configure DMA properties and ops from DT

On Mon, Feb 22, 2016 at 4:07 PM, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
> On Mon 22 Feb 02:03 PST 2016, Srinivas Kandagatla wrote:
>
>>
>>
>> On 22/02/16 05:32, Bjorn Andersson wrote:
>> >On certain platforms (e.g. ARM64) the dma_ops needs to be explicitly set
>> >to be able to do DMA allocations, so use the of_dma_configure() helper
>> >to populate the dma properties and assign an appropriate dma_ops.

We also hit the same issue with the dwc3 driver.

>> >
>> >Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>> >---
>> >  drivers/usb/chipidea/core.c | 4 ++++
>> >  1 file changed, 4 insertions(+)
>> >
>> >diff --git a/drivers/usb/chipidea/core.c b/drivers/usb/chipidea/core.c
>> >index 7404064b9bbc..047b9d4e67aa 100644
>> >--- a/drivers/usb/chipidea/core.c
>> >+++ b/drivers/usb/chipidea/core.c
>> >@@ -62,6 +62,7 @@
>> >  #include <linux/usb/chipidea.h>
>> >  #include <linux/usb/of.h>
>> >  #include <linux/of.h>
>> >+#include <linux/of_device.h>
>> >  #include <linux/phy.h>
>> >  #include <linux/regulator/consumer.h>
>> >  #include <linux/usb/ehci_def.h>
>> >@@ -834,6 +835,9 @@ struct platform_device *ci_hdrc_add_device(struct device *dev,
>> >     pdev->dev.dma_parms = dev->dma_parms;
>> >     dma_set_coherent_mask(&pdev->dev, dev->coherent_dma_mask);
>> >
>> >+    if (IS_ENABLED(CONFIG_OF) && dev->of_node)
>> >+            of_dma_configure(&pdev->dev, dev->of_node);
>> >+
>> Would we hit the same issue if we are on non Device tree platforms like ACPI
>> or platform device style itself?
>>
>
> As far as I can see, yes.
>
>>
>> >     ret = platform_device_add_resources(pdev, res, nres);
>> >     if (ret)
>> >             goto err;
>> >
>>
>> I think this is the side effect of commit
>> 1dccb598df549d892b6450c261da54cdd7af44b4(arm64: simplify dma_get_ops)
>>
>
> I agree, before that we would have hit:
>
> __generic_dma_ops() {
> ..
>        else if (acpi_disabled)
>                return dma_ops;
> ...
> }
>
> with dma_ops being swiotlb_dma_ops from arm64_dma_init().
>
>
> But this would not have saved us in the ACPI case, i.e. the result would
> have been as with my suggested patch. Poking Arnd here to see if he has
> any input.
>
>> None of the drivers call of_dma_configure() explicitly, which makes me feel
>> that we are doing something wrong. TBH, this should be handled in more
>> generic way rather than driver like this having an explicit call to
>> of_dma_configure().
>>
>
> I agree, trying to figure out if it should be inherited or something.

I also agree.  We need address it in a more generic way.  I did a
search for platform_device_add()/platform_device_register() in the
kernel source code.  I found a lot of them and many could be also
doing DMA.  Looks like it is still too early to assume every device is
already getting dma_ops set through bus probe.  Otherwise, many
drivers are potentially broken by this assumption.

Regards,
Leo