[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[Paul Cercueil]

Le sam. 7 juil. 2018 à 9:34, PrasannaKumar Muralidharan 
<prasannatsmkumar@gmail.com> a écrit :
> On 5 July 2018 at 23:56, Paul Cercueil <paul@crapouillou.net> wrote:
>>  Hi PrasannaKumar,
>> 
>> 
>>>  Hi Paul,
>>> 
>>>  On 3 July 2018 at 18:02, Paul Cercueil <paul@crapouillou.net> 
>>> wrote:
>>>> 
>>>>   As part of the work to support various other Ingenic JZ47xx SoC
>>>>  versions,
>>>>   which don't feature the same number of DMA channels per core, we 
>>>> now
>>>>   deduce the number of DMA channels available from the devicetree
>>>>   compatible string.
>>>> 
>>>>   Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>>>   ---
>>>>    drivers/dma/dma-jz4780.c | 53 
>>>> +++++++++++++++++++++++++++++-----------
>>>>    1 file changed, 39 insertions(+), 14 deletions(-)
>>>> 
>>>>   diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
>>>>   index 85820a2d69d4..b40f491f0367 100644
>>>>   --- a/drivers/dma/dma-jz4780.c
>>>>   +++ b/drivers/dma/dma-jz4780.c
>>>>   @@ -16,6 +16,7 @@
>>>>    #include <linux/interrupt.h>
>>>>    #include <linux/module.h>
>>>>    #include <linux/of.h>
>>>>   +#include <linux/of_device.h>
>>>>    #include <linux/of_dma.h>
>>>>    #include <linux/platform_device.h>
>>>>    #include <linux/slab.h>
>>>>   @@ -23,8 +24,6 @@
>>>>    #include "dmaengine.h"
>>>>    #include "virt-dma.h"
>>>> 
>>>>   -#define JZ_DMA_NR_CHANNELS     32
>>>>   -
>>>>    /* Global registers. */
>>>>    #define JZ_DMA_REG_DMAC                0x1000
>>>>    #define JZ_DMA_REG_DIRQP       0x1004
>>>>   @@ -135,14 +134,20 @@ struct jz4780_dma_chan {
>>>>           unsigned int curr_hwdesc;
>>>>    };
>>>> 
>>>>   +enum jz_version {
>>>>   +       ID_JZ4780,
>>>>   +};
>>>>   +
>>>>    struct jz4780_dma_dev {
>>>>           struct dma_device dma_device;
>>>>           void __iomem *base;
>>>>           struct clk *clk;
>>>>           unsigned int irq;
>>>>   +       unsigned int nb_channels;
>>>>   +       enum jz_version version;
>>>> 
>>>>           uint32_t chan_reserved;
>>>>   -       struct jz4780_dma_chan chan[JZ_DMA_NR_CHANNELS];
>>>>   +       struct jz4780_dma_chan chan[];
>>> 
>>> 
>>>  Looks like a variable length array in struct. I think there is some
>>>  effort to remove the usage of VLA. Can you revisit this? I may be
>>>  wrong, please feel free to correct.
>> 
>> 
>>  Are you sure? It's the first time I hear about it.
>>  Could anybody confirm?
> 
> Please see [1] for info.
> 
> Variable Length Arrays in struct is expressly forbidden in C99, C11.
> Clang does not support it. To make kernel compile with Clang few
> people are trying to remove/reduce VLAIS usage.
> 
> 1. 
> https://blog.linuxplumbersconf.org/2013/ocw/system/presentations/1221/original/VLAIS.pdf

I read it, and my structure is not a VLAIS; my "chan" array is a 
flexible
array, its sizeof() is 0, so the sizeof() of the structure is constant.

See page 6 of the PDF, about alternatives to VLAIS:
"If possible use a flexible array member and move the array to the end 
of
the struct"
Which is what I am doing here.

-Paul
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[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[Vinod Koul]

Hi Paul,

On 10-07-18, 17:29, Paul Cercueil wrote:
> > >  +static const unsigned int jz4780_dma_nb_channels[] = {
> > >  +	[ID_JZ4780] = 32,
> > >  +};
> > >  +
> > >  +static const struct of_device_id jz4780_dma_dt_match[] = {
> > >  +	{ .compatible = "ingenic,jz4780-dma", .data = (void *)ID_JZ4780 },
> > >  +	{},
> > >  +};
> > 
> > Looking at description I was hoping that channels would be in DT,
> > channels is hardware information, so should come from DT rather than
> > coding the kernel...
> 
> I had a talk with Linus Walleij (GPIO maintainer) about that:
> http://lkml.iu.edu/hypermail/linux/kernel/1701.3/05422.html
> 
> And I agree with him, we shouldn't have in devicetree what we can deduce
> from the compatible string. But there doesn't seem to be an enforced
> policy about it.

Looking at this, yes that can be done as you have implemented but adding
new compatible and tables every time seems not so great to me.

If DT can describe these hardware features then driver can take action generically
and we avoid these tables and skip some patches here..

> 
> @Rob, what do you think?

Rob what is the recommendation here?

> 
> > >  -	jzdma = devm_kzalloc(dev, sizeof(*jzdma), GFP_KERNEL);
> > >  +	if (of_id)
> > >  +		version = (enum jz_version)of_id->data;
> > >  +	else
> > >  +		version = ID_JZ4780; /* Default when not probed from DT */
> > 
> > where else would it be probed from.... ?
> 
> Platform, MFD driver, etc. But not likely to happen.
> I can remove these lines if you want.

Lets add when we land support for those.

[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[Vinod Koul]

On 03-07-18, 14:32, Paul Cercueil wrote:

>  struct jz4780_dma_dev {
>  	struct dma_device dma_device;
>  	void __iomem *base;
>  	struct clk *clk;
>  	unsigned int irq;
> +	unsigned int nb_channels;
> +	enum jz_version version;
>  
>  	uint32_t chan_reserved;
> -	struct jz4780_dma_chan chan[JZ_DMA_NR_CHANNELS];
> +	struct jz4780_dma_chan chan[];

why array, why not channel pointer?

> +static const unsigned int jz4780_dma_nb_channels[] = {
> +	[ID_JZ4780] = 32,
> +};
> +
> +static const struct of_device_id jz4780_dma_dt_match[] = {
> +	{ .compatible = "ingenic,jz4780-dma", .data = (void *)ID_JZ4780 },
> +	{},
> +};

Looking at description I was hoping that channels would be in DT,
channels is hardware information, so should come from DT rather than
coding the kernel...

> -	jzdma = devm_kzalloc(dev, sizeof(*jzdma), GFP_KERNEL);
> +	if (of_id)
> +		version = (enum jz_version)of_id->data;
> +	else
> +		version = ID_JZ4780; /* Default when not probed from DT */

where else would it be probed from.... ?

[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[PrasannaKumar Muralidharan]

On 5 July 2018 at 23:56, Paul Cercueil <paul@crapouillou.net> wrote:
> Hi PrasannaKumar,
>
>
>> Hi Paul,
>>
>> On 3 July 2018 at 18:02, Paul Cercueil <paul@crapouillou.net> wrote:
>>>
>>>  As part of the work to support various other Ingenic JZ47xx SoC
>>> versions,
>>>  which don't feature the same number of DMA channels per core, we now
>>>  deduce the number of DMA channels available from the devicetree
>>>  compatible string.
>>>
>>>  Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>>  ---
>>>   drivers/dma/dma-jz4780.c | 53 +++++++++++++++++++++++++++++-----------
>>>   1 file changed, 39 insertions(+), 14 deletions(-)
>>>
>>>  diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
>>>  index 85820a2d69d4..b40f491f0367 100644
>>>  --- a/drivers/dma/dma-jz4780.c
>>>  +++ b/drivers/dma/dma-jz4780.c
>>>  @@ -16,6 +16,7 @@
>>>   #include <linux/interrupt.h>
>>>   #include <linux/module.h>
>>>   #include <linux/of.h>
>>>  +#include <linux/of_device.h>
>>>   #include <linux/of_dma.h>
>>>   #include <linux/platform_device.h>
>>>   #include <linux/slab.h>
>>>  @@ -23,8 +24,6 @@
>>>   #include "dmaengine.h"
>>>   #include "virt-dma.h"
>>>
>>>  -#define JZ_DMA_NR_CHANNELS     32
>>>  -
>>>   /* Global registers. */
>>>   #define JZ_DMA_REG_DMAC                0x1000
>>>   #define JZ_DMA_REG_DIRQP       0x1004
>>>  @@ -135,14 +134,20 @@ struct jz4780_dma_chan {
>>>          unsigned int curr_hwdesc;
>>>   };
>>>
>>>  +enum jz_version {
>>>  +       ID_JZ4780,
>>>  +};
>>>  +
>>>   struct jz4780_dma_dev {
>>>          struct dma_device dma_device;
>>>          void __iomem *base;
>>>          struct clk *clk;
>>>          unsigned int irq;
>>>  +       unsigned int nb_channels;
>>>  +       enum jz_version version;
>>>
>>>          uint32_t chan_reserved;
>>>  -       struct jz4780_dma_chan chan[JZ_DMA_NR_CHANNELS];
>>>  +       struct jz4780_dma_chan chan[];
>>
>>
>> Looks like a variable length array in struct. I think there is some
>> effort to remove the usage of VLA. Can you revisit this? I may be
>> wrong, please feel free to correct.
>
>
> Are you sure? It's the first time I hear about it.
> Could anybody confirm?

Please see [1] for info.

Variable Length Arrays in struct is expressly forbidden in C99, C11.
Clang does not support it. To make kernel compile with Clang few
people are trying to remove/reduce VLAIS usage.

1. https://blog.linuxplumbersconf.org/2013/ocw/system/presentations/1221/original/VLAIS.pdf
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[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[Paul Cercueil]

Hi PrasannaKumar,

> Hi Paul,
> 
> On 3 July 2018 at 18:02, Paul Cercueil <paul@crapouillou.net> wrote:
>>  As part of the work to support various other Ingenic JZ47xx SoC 
>> versions,
>>  which don't feature the same number of DMA channels per core, we now
>>  deduce the number of DMA channels available from the devicetree
>>  compatible string.
>> 
>>  Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>  ---
>>   drivers/dma/dma-jz4780.c | 53 
>> +++++++++++++++++++++++++++++-----------
>>   1 file changed, 39 insertions(+), 14 deletions(-)
>> 
>>  diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
>>  index 85820a2d69d4..b40f491f0367 100644
>>  --- a/drivers/dma/dma-jz4780.c
>>  +++ b/drivers/dma/dma-jz4780.c
>>  @@ -16,6 +16,7 @@
>>   #include <linux/interrupt.h>
>>   #include <linux/module.h>
>>   #include <linux/of.h>
>>  +#include <linux/of_device.h>
>>   #include <linux/of_dma.h>
>>   #include <linux/platform_device.h>
>>   #include <linux/slab.h>
>>  @@ -23,8 +24,6 @@
>>   #include "dmaengine.h"
>>   #include "virt-dma.h"
>> 
>>  -#define JZ_DMA_NR_CHANNELS     32
>>  -
>>   /* Global registers. */
>>   #define JZ_DMA_REG_DMAC                0x1000
>>   #define JZ_DMA_REG_DIRQP       0x1004
>>  @@ -135,14 +134,20 @@ struct jz4780_dma_chan {
>>          unsigned int curr_hwdesc;
>>   };
>> 
>>  +enum jz_version {
>>  +       ID_JZ4780,
>>  +};
>>  +
>>   struct jz4780_dma_dev {
>>          struct dma_device dma_device;
>>          void __iomem *base;
>>          struct clk *clk;
>>          unsigned int irq;
>>  +       unsigned int nb_channels;
>>  +       enum jz_version version;
>> 
>>          uint32_t chan_reserved;
>>  -       struct jz4780_dma_chan chan[JZ_DMA_NR_CHANNELS];
>>  +       struct jz4780_dma_chan chan[];
> 
> Looks like a variable length array in struct. I think there is some
> effort to remove the usage of VLA. Can you revisit this? I may be
> wrong, please feel free to correct.

Are you sure? It's the first time I hear about it.
Could anybody confirm?

>>   };
>> 
>>   struct jz4780_dma_filter_data {
>>  @@ -648,7 +653,7 @@ static irqreturn_t jz4780_dma_irq_handler(int 
>> irq, void *data)
>> 
>>          pending = jz4780_dma_readl(jzdma, JZ_DMA_REG_DIRQP);
>> 
>>  -       for (i = 0; i < JZ_DMA_NR_CHANNELS; i++) {
>>  +       for (i = 0; i < jzdma->nb_channels; i++) {
>>                  if (!(pending & (1<<i)))
>>                          continue;
>> 
>>  @@ -728,7 +733,7 @@ static struct dma_chan 
>> *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
>>          data.channel = dma_spec->args[1];
>> 
>>          if (data.channel > -1) {
>>  -               if (data.channel >= JZ_DMA_NR_CHANNELS) {
>>  +               if (data.channel >= jzdma->nb_channels) {
>>                          dev_err(jzdma->dma_device.dev,
>>                                  "device requested non-existent 
>> channel %u\n",
>>                                  data.channel);
>>  @@ -752,19 +757,45 @@ static struct dma_chan 
>> *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
>>          }
>>   }
>> 
>>  +static const unsigned int jz4780_dma_nb_channels[] = {
>>  +       [ID_JZ4780] = 32,
>>  +};
>>  +
>>  +static const struct of_device_id jz4780_dma_dt_match[] = {
>>  +       { .compatible = "ingenic,jz4780-dma", .data = (void 
>> *)ID_JZ4780 },
>>  +       {},
>>  +};
>>  +MODULE_DEVICE_TABLE(of, jz4780_dma_dt_match);
>>  +
>>   static int jz4780_dma_probe(struct platform_device *pdev)
>>   {
>>          struct device *dev = &pdev->dev;
>>  +       const struct of_device_id *of_id = of_match_device(
>>  +                       jz4780_dma_dt_match, dev);
>>          struct jz4780_dma_dev *jzdma;
>>          struct jz4780_dma_chan *jzchan;
>>          struct dma_device *dd;
>>          struct resource *res;
>>  +       enum jz_version version;
>>  +       unsigned int nb_channels;
>>          int i, ret;
>> 
>>  -       jzdma = devm_kzalloc(dev, sizeof(*jzdma), GFP_KERNEL);
>>  +       if (of_id)
>>  +               version = (enum jz_version)of_id->data;
>>  +       else
>>  +               version = ID_JZ4780; /* Default when not probed 
>> from DT */
>>  +
>>  +       nb_channels = jz4780_dma_nb_channels[version];
>>  +
>>  +       jzdma = devm_kzalloc(dev, sizeof(*jzdma)
>>  +                               + sizeof(*jzdma->chan) * 
>> nb_channels,
>>  +                               GFP_KERNEL);
>>          if (!jzdma)
>>                  return -ENOMEM;
>> 
>>  +       jzdma->nb_channels = nb_channels;
>>  +       jzdma->version = version;
>>  +
>>          platform_set_drvdata(pdev, jzdma);
>> 
>>          res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>  @@ -839,7 +870,7 @@ static int jz4780_dma_probe(struct 
>> platform_device *pdev)
>> 
>>          INIT_LIST_HEAD(&dd->channels);
>> 
>>  -       for (i = 0; i < JZ_DMA_NR_CHANNELS; i++) {
>>  +       for (i = 0; i < jzdma->nb_channels; i++) {
>>                  jzchan = &jzdma->chan[i];
>>                  jzchan->id = i;
>> 
>>  @@ -884,19 +915,13 @@ static int jz4780_dma_remove(struct 
>> platform_device *pdev)
>> 
>>          free_irq(jzdma->irq, jzdma);
>> 
>>  -       for (i = 0; i < JZ_DMA_NR_CHANNELS; i++)
>>  +       for (i = 0; i < jzdma->nb_channels; i++)
>>                  tasklet_kill(&jzdma->chan[i].vchan.task);
>> 
>>          dma_async_device_unregister(&jzdma->dma_device);
>>          return 0;
>>   }
>> 
>>  -static const struct of_device_id jz4780_dma_dt_match[] = {
>>  -       { .compatible = "ingenic,jz4780-dma", .data = NULL },
>>  -       {},
>>  -};
>>  -MODULE_DEVICE_TABLE(of, jz4780_dma_dt_match);
>>  -
>>   static struct platform_driver jz4780_dma_driver = {
>>          .probe          = jz4780_dma_probe,
>>          .remove         = jz4780_dma_remove,
>>  --
>>  2.18.0
>> 
>>
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[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[PrasannaKumar Muralidharan]

Hi Paul,

On 3 July 2018 at 18:02, Paul Cercueil <paul@crapouillou.net> wrote:
> As part of the work to support various other Ingenic JZ47xx SoC versions,
> which don't feature the same number of DMA channels per core, we now
> deduce the number of DMA channels available from the devicetree
> compatible string.
>
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> ---
>  drivers/dma/dma-jz4780.c | 53 +++++++++++++++++++++++++++++-----------
>  1 file changed, 39 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
> index 85820a2d69d4..b40f491f0367 100644
> --- a/drivers/dma/dma-jz4780.c
> +++ b/drivers/dma/dma-jz4780.c
> @@ -16,6 +16,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/of_device.h>
>  #include <linux/of_dma.h>
>  #include <linux/platform_device.h>
>  #include <linux/slab.h>
> @@ -23,8 +24,6 @@
>  #include "dmaengine.h"
>  #include "virt-dma.h"
>
> -#define JZ_DMA_NR_CHANNELS     32
> -
>  /* Global registers. */
>  #define JZ_DMA_REG_DMAC                0x1000
>  #define JZ_DMA_REG_DIRQP       0x1004
> @@ -135,14 +134,20 @@ struct jz4780_dma_chan {
>         unsigned int curr_hwdesc;
>  };
>
> +enum jz_version {
> +       ID_JZ4780,
> +};
> +
>  struct jz4780_dma_dev {
>         struct dma_device dma_device;
>         void __iomem *base;
>         struct clk *clk;
>         unsigned int irq;
> +       unsigned int nb_channels;
> +       enum jz_version version;
>
>         uint32_t chan_reserved;
> -       struct jz4780_dma_chan chan[JZ_DMA_NR_CHANNELS];
> +       struct jz4780_dma_chan chan[];

Looks like a variable length array in struct. I think there is some
effort to remove the usage of VLA. Can you revisit this? I may be
wrong, please feel free to correct.

>  };
>
>  struct jz4780_dma_filter_data {
> @@ -648,7 +653,7 @@ static irqreturn_t jz4780_dma_irq_handler(int irq, void *data)
>
>         pending = jz4780_dma_readl(jzdma, JZ_DMA_REG_DIRQP);
>
> -       for (i = 0; i < JZ_DMA_NR_CHANNELS; i++) {
> +       for (i = 0; i < jzdma->nb_channels; i++) {
>                 if (!(pending & (1<<i)))
>                         continue;
>
> @@ -728,7 +733,7 @@ static struct dma_chan *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
>         data.channel = dma_spec->args[1];
>
>         if (data.channel > -1) {
> -               if (data.channel >= JZ_DMA_NR_CHANNELS) {
> +               if (data.channel >= jzdma->nb_channels) {
>                         dev_err(jzdma->dma_device.dev,
>                                 "device requested non-existent channel %u\n",
>                                 data.channel);
> @@ -752,19 +757,45 @@ static struct dma_chan *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
>         }
>  }
>
> +static const unsigned int jz4780_dma_nb_channels[] = {
> +       [ID_JZ4780] = 32,
> +};
> +
> +static const struct of_device_id jz4780_dma_dt_match[] = {
> +       { .compatible = "ingenic,jz4780-dma", .data = (void *)ID_JZ4780 },
> +       {},
> +};
> +MODULE_DEVICE_TABLE(of, jz4780_dma_dt_match);
> +
>  static int jz4780_dma_probe(struct platform_device *pdev)
>  {
>         struct device *dev = &pdev->dev;
> +       const struct of_device_id *of_id = of_match_device(
> +                       jz4780_dma_dt_match, dev);
>         struct jz4780_dma_dev *jzdma;
>         struct jz4780_dma_chan *jzchan;
>         struct dma_device *dd;
>         struct resource *res;
> +       enum jz_version version;
> +       unsigned int nb_channels;
>         int i, ret;
>
> -       jzdma = devm_kzalloc(dev, sizeof(*jzdma), GFP_KERNEL);
> +       if (of_id)
> +               version = (enum jz_version)of_id->data;
> +       else
> +               version = ID_JZ4780; /* Default when not probed from DT */
> +
> +       nb_channels = jz4780_dma_nb_channels[version];
> +
> +       jzdma = devm_kzalloc(dev, sizeof(*jzdma)
> +                               + sizeof(*jzdma->chan) * nb_channels,
> +                               GFP_KERNEL);
>         if (!jzdma)
>                 return -ENOMEM;
>
> +       jzdma->nb_channels = nb_channels;
> +       jzdma->version = version;
> +
>         platform_set_drvdata(pdev, jzdma);
>
>         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> @@ -839,7 +870,7 @@ static int jz4780_dma_probe(struct platform_device *pdev)
>
>         INIT_LIST_HEAD(&dd->channels);
>
> -       for (i = 0; i < JZ_DMA_NR_CHANNELS; i++) {
> +       for (i = 0; i < jzdma->nb_channels; i++) {
>                 jzchan = &jzdma->chan[i];
>                 jzchan->id = i;
>
> @@ -884,19 +915,13 @@ static int jz4780_dma_remove(struct platform_device *pdev)
>
>         free_irq(jzdma->irq, jzdma);
>
> -       for (i = 0; i < JZ_DMA_NR_CHANNELS; i++)
> +       for (i = 0; i < jzdma->nb_channels; i++)
>                 tasklet_kill(&jzdma->chan[i].vchan.task);
>
>         dma_async_device_unregister(&jzdma->dma_device);
>         return 0;
>  }
>
> -static const struct of_device_id jz4780_dma_dt_match[] = {
> -       { .compatible = "ingenic,jz4780-dma", .data = NULL },
> -       {},
> -};
> -MODULE_DEVICE_TABLE(of, jz4780_dma_dt_match);
> -
>  static struct platform_driver jz4780_dma_driver = {
>         .probe          = jz4780_dma_probe,
>         .remove         = jz4780_dma_remove,
> --
> 2.18.0
>
>
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[01/14] dmaengine: dma-jz4780: Avoid hardcoding number of channels

[Paul Cercueil]

As part of the work to support various other Ingenic JZ47xx SoC versions,
which don't feature the same number of DMA channels per core, we now
deduce the number of DMA channels available from the devicetree
compatible string.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
---
 drivers/dma/dma-jz4780.c | 53 +++++++++++++++++++++++++++++-----------
 1 file changed, 39 insertions(+), 14 deletions(-)

diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
index 85820a2d69d4..b40f491f0367 100644
--- a/drivers/dma/dma-jz4780.c
+++ b/drivers/dma/dma-jz4780.c
@@ -16,6 +16,7 @@
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_device.h>
 #include <linux/of_dma.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
@@ -23,8 +24,6 @@
 #include "dmaengine.h"
 #include "virt-dma.h"
 
-#define JZ_DMA_NR_CHANNELS	32
-
 /* Global registers. */
 #define JZ_DMA_REG_DMAC		0x1000
 #define JZ_DMA_REG_DIRQP	0x1004
@@ -135,14 +134,20 @@ struct jz4780_dma_chan {
 	unsigned int curr_hwdesc;
 };
 
+enum jz_version {
+	ID_JZ4780,
+};
+
 struct jz4780_dma_dev {
 	struct dma_device dma_device;
 	void __iomem *base;
 	struct clk *clk;
 	unsigned int irq;
+	unsigned int nb_channels;
+	enum jz_version version;
 
 	uint32_t chan_reserved;
-	struct jz4780_dma_chan chan[JZ_DMA_NR_CHANNELS];
+	struct jz4780_dma_chan chan[];
 };
 
 struct jz4780_dma_filter_data {
@@ -648,7 +653,7 @@ static irqreturn_t jz4780_dma_irq_handler(int irq, void *data)
 
 	pending = jz4780_dma_readl(jzdma, JZ_DMA_REG_DIRQP);
 
-	for (i = 0; i < JZ_DMA_NR_CHANNELS; i++) {
+	for (i = 0; i < jzdma->nb_channels; i++) {
 		if (!(pending & (1<<i)))
 			continue;
 
@@ -728,7 +733,7 @@ static struct dma_chan *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
 	data.channel = dma_spec->args[1];
 
 	if (data.channel > -1) {
-		if (data.channel >= JZ_DMA_NR_CHANNELS) {
+		if (data.channel >= jzdma->nb_channels) {
 			dev_err(jzdma->dma_device.dev,
 				"device requested non-existent channel %u\n",
 				data.channel);
@@ -752,19 +757,45 @@ static struct dma_chan *jz4780_of_dma_xlate(struct of_phandle_args *dma_spec,
 	}
 }
 
+static const unsigned int jz4780_dma_nb_channels[] = {
+	[ID_JZ4780] = 32,
+};
+
+static const struct of_device_id jz4780_dma_dt_match[] = {
+	{ .compatible = "ingenic,jz4780-dma", .data = (void *)ID_JZ4780 },
+	{},
+};
+MODULE_DEVICE_TABLE(of, jz4780_dma_dt_match);
+
 static int jz4780_dma_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
+	const struct of_device_id *of_id = of_match_device(
+			jz4780_dma_dt_match, dev);
 	struct jz4780_dma_dev *jzdma;
 	struct jz4780_dma_chan *jzchan;
 	struct dma_device *dd;
 	struct resource *res;
+	enum jz_version version;
+	unsigned int nb_channels;
 	int i, ret;
 
-	jzdma = devm_kzalloc(dev, sizeof(*jzdma), GFP_KERNEL);
+	if (of_id)
+		version = (enum jz_version)of_id->data;
+	else
+		version = ID_JZ4780; /* Default when not probed from DT */
+
+	nb_channels = jz4780_dma_nb_channels[version];
+
+	jzdma = devm_kzalloc(dev, sizeof(*jzdma)
+				+ sizeof(*jzdma->chan) * nb_channels,
+				GFP_KERNEL);
 	if (!jzdma)
 		return -ENOMEM;
 
+	jzdma->nb_channels = nb_channels;
+	jzdma->version = version;
+
 	platform_set_drvdata(pdev, jzdma);
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
@@ -839,7 +870,7 @@ static int jz4780_dma_probe(struct platform_device *pdev)
 
 	INIT_LIST_HEAD(&dd->channels);
 
-	for (i = 0; i < JZ_DMA_NR_CHANNELS; i++) {
+	for (i = 0; i < jzdma->nb_channels; i++) {
 		jzchan = &jzdma->chan[i];
 		jzchan->id = i;
 
@@ -884,19 +915,13 @@ static int jz4780_dma_remove(struct platform_device *pdev)
 
 	free_irq(jzdma->irq, jzdma);
 
-	for (i = 0; i < JZ_DMA_NR_CHANNELS; i++)
+	for (i = 0; i < jzdma->nb_channels; i++)
 		tasklet_kill(&jzdma->chan[i].vchan.task);
 
 	dma_async_device_unregister(&jzdma->dma_device);
 	return 0;
 }
 
-static const struct of_device_id jz4780_dma_dt_match[] = {
-	{ .compatible = "ingenic,jz4780-dma", .data = NULL },
-	{},
-};
-MODULE_DEVICE_TABLE(of, jz4780_dma_dt_match);
-
 static struct platform_driver jz4780_dma_driver = {
 	.probe		= jz4780_dma_probe,
 	.remove		= jz4780_dma_remove,