linux-kernel - Re: [PATCH 1/2] dma: add Qualcomm Technologies HIDMA management driver

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Date:	Fri, 30 Oct 2015 19:59:53 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Sinan Kaya <okaya@...eaurora.org>,
	dmaengine <dmaengine@...r.kernel.org>, timur@...eaurora.org,
	cov@...eaurora.org, jcm@...hat.com,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	devicetree <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dma: add Qualcomm Technologies HIDMA management driver

On Fri, Oct 30, 2015 at 5:00 PM, Mark Rutland <mark.rutland@....com> wrote:
> On Thu, Oct 29, 2015 at 11:08:12PM -0400, Sinan Kaya wrote:
>> The Qualcomm Technologies HIDMA device has been designed
>> to support virtualization technology. The driver has been
>> divided into two to follow the hardware design. The management
>> driver is executed in hypervisor context and is the main
>> managment for all channels provided by the device. The
>> channel driver is exected in the guest OS context.
>>

>> +#if IS_ENABLED(CONFIG_ACPI)
>> +static const struct acpi_device_id qcom_hidma_mgmt_acpi_ids[] = {
>> +     {"QCOM8060"},
>> +     {},
>> +};
>> +#endif
>
> How do DMA engines work with ACPI?
>
> How are client relationships defined?

The ACPI tables DSDT and CSRT (more info here:
http://www.acpi.info/links.htm) defines properties.

DSDT:
 per DMAC: the resources
 per client: FixedDMA descriptor that contains channel / request line pair.

CSRT:
 necessary table to map which DMAC provides which request line, thus
request line numbering are global on platform.

When DMAC driver is probed in the running system it should call as
well registration function from acpi-dma.c.

All clients when use new DMA slave API gets channel automatically
based on their FixedDMA property.

So, above is how it should be done. Didn't actually checked what this
driver does.

-- 
With Best Regards,
Andy Shevchenko
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