Re: [PATCH v3 4/7] of: configure the platform device dma parameters

Santosh Shilimkar
2014-05-07T13:24:57Z

On Tuesday 06 May 2014 04:44 PM, Santosh Shilimkar wrote:
> On Tuesday 06 May 2014 05:40 AM, Arnd Bergmann wrote:
>> On Monday 05 May 2014 17:47:32 Santosh Shilimkar wrote:
>>
>>> + dev->coherent_dma_mask = DMA_BIT_MASK(32);
>>> + if (!dev->dma_mask)
>>> + dev->dma_mask = &dev->coherent_dma_mask;
>>> +
>>> + /*
>>> + * if dma-ranges property doesn't exist - just return else
>>> + * setup the dma offset
>>> + */
>>> + ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>>> + if (ret < 0) {
>>> + dev_dbg(dev, "no dma range information to setup\n");
>>> + return;
>>> + }
>>> +
>>> + /* DMA ranges found. Calculate and set dma_pfn_offset */
>>> + dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
>>> + dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
>>> +}
>>
>> I think there should at least be a comment about why we are computing
>> the correct DMA mask here and then ignore that and just use DMA_BIT_MASK(32)
>> instead. I understand that Russell and Rob prefer it that way and I'm not
>> going to argue, but I find it counterintuitive and I think it deserves
>> an explanation in the source code for anybody who is trying to figure
>> out how things fit together.
>>
> In this patch, the dma_mask related code is just moved. We are not calculating
> dma_mask either. I was looking for the history of how DMA_BIT_MASK(32)
> landed up but couldn't trace it down apart from the fact that the code was
> carried from powerPC. May be Rob knows.
>
> How about below comment ? I didn't delibratly added point about bus
> intercepting drivers dma_set_*mask() call etc.
>
> /*
> * Set default dma-mask to 32 bit. Drivers are expected to setup
> * the correct supported dma_mask.
> */
> + dev->coherent_dma_mask = DMA_BIT_MASK(32);
> + if (!dev->dma_mask)
> + dev->dma_mask = &dev->coherent_dma_mask;
>
Updated patch below for records.

>From 591c1ee465ce5372385dbc41e7d3e36cbb477bd8 Mon Sep 17 00:00:00 2001
From: Santosh Shilimkar <santosh.shilimkar@ti.com>
Date: Thu, 24 Apr 2014 11:30:04 -0400
Subject: [PATCH v3 4/7] of: configure the platform device dma parameters

Retrieve DMA configuration from DT and setup platform device's DMA
parameters. The DMA configuration in DT has to be specified using
"dma-ranges" and "dma-coherent" properties if supported.

We setup dma_pfn_offset using "dma-ranges" and dma_coherent_ops
using "dma-coherent" device tree properties.

The set_arch_dma_coherent_ops macro has to be defined by arch if
it supports coherent dma_ops. Otherwise, set_arch_dma_coherent_ops() is
declared as nop.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Olof Johansson <olof@lixom.net>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
---
drivers/of/platform.c | 65 +++++++++++++++++++++++++++++++++++++++----
include/linux/dma-mapping.h | 7 +++++
2 files changed, 66 insertions(+), 6 deletions(-)

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 404d1da..91fa983 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -187,6 +187,64 @@ struct platform_device *of_device_alloc(struct device_node *np,
EXPORT_SYMBOL(of_device_alloc);

/**
+ * of_dma_configure - Setup DMA configuration
+ * @dev: Device to apply DMA configuration
+ *
+ * Try to get devices's DMA configuration from DT and update it
+ * accordingly.
+ *
+ * In case if platform code need to use own special DMA configuration,it
+ * can use Platform bus notifier and handle BUS_NOTIFY_ADD_DEVICE event
+ * to fix up DMA configuration.
+ */
+static void of_dma_configure(struct platform_device *pdev)
+{
+ u64 dma_addr, paddr, size;
+ int ret;
+ struct device *dev = &pdev->dev;
+
+#if defined(CONFIG_MICROBLAZE)
+ pdev->archdata.dma_mask = 0xffffffffUL;
+#endif
+
+ /*
+ * Set default dma-mask to 32 bit. Drivers are expected to setup
+ * the correct supported dma_mask.
+ */
+ dev->coherent_dma_mask = DMA_BIT_MASK(32);
+
+ /*
+ * Set it to coherent_dma_mask by default if the architecture
+ * code has not set it.
+ */
+ if (!dev->dma_mask)
+ dev->dma_mask = &dev->coherent_dma_mask;
+
+ /*
+ * if dma-coherent property exist, call arch hook to setup
+ * dma coherent operations.
+ */
+ if (of_dma_is_coherent(dev->of_node)) {
+ set_arch_dma_coherent_ops(dev);
+ dev_dbg(dev, "device is dma coherent\n");
+ }
+
+ /*
+ * if dma-ranges property doesn't exist - just return else
+ * setup the dma offset
+ */
+ ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
+ if (ret < 0) {
+ dev_dbg(dev, "no dma range information to setup\n");
+ return;
+ }
+
+ /* DMA ranges found. Calculate and set dma_pfn_offset */
+ dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
+ dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
+}
+
+/**
* of_platform_device_create_pdata - Alloc, initialize and register an of_device
* @np: pointer to node to create device for
* @bus_id: name to assign device
@@ -211,12 +269,7 @@ static struct platform_device *of_platform_device_create_pdata(
if (!dev)
return NULL;

-#if defined(CONFIG_MICROBLAZE)
- dev->archdata.dma_mask = 0xffffffffUL;
-#endif
- dev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
- if (!dev->dev.dma_mask)
- dev->dev.dma_mask = &dev->dev.coherent_dma_mask;
+ of_dma_configure(dev);
dev->dev.bus = &platform_bus_type;
dev->dev.platform_data = platform_data;

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index fd4aee2..c7d9b1b 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -123,6 +123,13 @@ static inline int dma_coerce_mask_and_coherent(struct device *dev, u64 mask)

extern u64 dma_get_required_mask(struct device *dev);

+#ifndef set_arch_dma_coherent_ops
+static inline int set_arch_dma_coherent_ops(struct device *dev)
+{
+ return 0;
+}
+#endif
+
static inline unsigned int dma_get_max_seg_size(struct device *dev)
{
return dev->dma_parms ? dev->dma_parms->max_segment_size : 65536;
--
1.7.9.5