On 5 July 2018 at 23:56, Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
> Hi PrasannaKumar,
>
>
>> Hi Paul,
>>
>> On 3 July 2018 at 18:02, Paul Cercueil <paul@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
>>> ---
>>> 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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