linux-kernel - Re: [PATCH 2/2] acpi-dma: Add support for "dma-names" device property

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Date:	Tue, 15 Sep 2015 01:19:59 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] acpi-dma: Add support for "dma-names" device property

On Monday, September 14, 2015 05:37:36 PM Mika Westerberg wrote:
> The current implementation hard codes the two supported channels so that
> "tx" is always 0 and "rx" is always 1. This is because there has been no
> suitable way in ACPI to name resources.
> 
> With _DSD device properties we can finally do this:
> 
> 	Device (SPI1) {
> 	    Name (_CRS, ResourceTemplate () {
> 	        ...
> 	        FixedDMA (0x0000, 0x0000, Width32bit)
> 	        FixedDMA (0x0001, 0x0001, Width32bit)
> 	    })
> 
> 	    Name (_DSD, Package () {
> 	        ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> 	        Package () {
> 	            Package () {"dma-names", Package () {"tx", "rx"}}
> 	        },
> 	    })
> 	}
> 
> The names "tx" and "rx" now provide index of the FixedDMA resource in
> question.
> 
> Modify acpi_dma_request_slave_chan_by_name() so that it looks for
> "dma-names" property first and only then fall back using hardcoded indices.
> 
> The DT "dma-names" binding that we reuse for ACPI is documented in
> Documentation/devicetree/bindings/dma/dma.txt.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

This and the [1/2] both look reasonable to me, but I need an ACK from Vinod
for this one.

> ---
>  drivers/dma/acpi-dma.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/acpi-dma.c b/drivers/dma/acpi-dma.c
> index 5a635646e05c..981a38fc4cb8 100644
> --- a/drivers/dma/acpi-dma.c
> +++ b/drivers/dma/acpi-dma.c
> @@ -21,6 +21,7 @@
>  #include <linux/ioport.h>
>  #include <linux/acpi.h>
>  #include <linux/acpi_dma.h>
> +#include <linux/property.h>
>  
>  static LIST_HEAD(acpi_dma_list);
>  static DEFINE_MUTEX(acpi_dma_lock);
> @@ -413,21 +414,29 @@ EXPORT_SYMBOL_GPL(acpi_dma_request_slave_chan_by_index);
>   * translate the names "tx" and "rx" here based on the most common case where
>   * the first FixedDMA descriptor is TX and second is RX.
>   *
> + * If the device has "dma-names" property the FixedDMA descriptor indices
> + * are retrieved based on those. Otherwise the function falls back using
> + * hardcoded indices.
> + *
>   * Return:
>   * Pointer to appropriate dma channel on success or an error pointer.
>   */
>  struct dma_chan *acpi_dma_request_slave_chan_by_name(struct device *dev,
>  		const char *name)
>  {
> -	size_t index;
> -
> -	if (!strcmp(name, "tx"))
> -		index = 0;
> -	else if (!strcmp(name, "rx"))
> -		index = 1;
> -	else
> -		return ERR_PTR(-ENODEV);
> +	int index;
> +
> +	index = device_property_match_string(dev, "dma-names", name);
> +	if (index < 0) {
> +		if (!strcmp(name, "tx"))
> +			index = 0;
> +		else if (!strcmp(name, "rx"))
> +			index = 1;
> +		else
> +			return ERR_PTR(-ENODEV);
> +	}
>  
> +	dev_dbg(dev, "found DMA channel \"%s\" at index %d\n", name, index);
>  	return acpi_dma_request_slave_chan_by_index(dev, index);
>  }
>  EXPORT_SYMBOL_GPL(acpi_dma_request_slave_chan_by_name);
> 

Thanks,
Rafael

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