RTEMS | bsp/aarch64/raspberrypi: Add support for DMA (!662)

[Christian Mauderer (@c-mauderer)]

Merge request https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662 was reviewed by Christian Mauderer

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Christian Mauderer started a new discussion on bsps/aarch64/raspberrypi/include/bsp/raspberrypi-dma.h: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662#note_129007

 > +} rpi_dma_channel;
 > +
 > +void* rpi_unaligned_mem_to_mem_dma( rpi_dma_channel channel, void *src, uint32_t length );

Please add a short doxygen description for all public functions. Only a short description what they should do and what the parameters are. Two or three sentences is usually quite useful already. For example for this function it could be:

```
Copies @a length bytes of data from @a src to some randomly allocated
location. Use the DMA @a channel for that. @returns the random location.
It's the callers responsibility to free the returned location.
```

PS: Regarding the destination of this special function: Please also take a look at the comment from Kinseys in the C file. It's not really useful for a user to copy a memory to some random location.

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Christian Mauderer started a new discussion on bsps/aarch64/raspberrypi/include/bsp/raspberrypi-dma.h: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662#note_129008

 > + * @file
 > + *
 > + * @ingroup raspberrypi_4_dma

Where do you define that Doxygen group? The Doxygen guide links to two examples:

https://docs.rtems.org/docs/main/eng/coding-doxygen.html#header-file-examples

I would suggest to use the same method like in this file:

[https://gitlab.rtems.org/rtems/rtos/rtems/-/blob/main/cpukit/include/rtems/score/thread.h](https://gitlab.rtems.org/rtems/rtos/rtems/-/blob/main/cpukit/include/rtems/score/thread.h#L79)

Your `ingroup` would be some raspberrypi group. Check the other files in the BSP for that.

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Christian Mauderer started a new discussion on bsps/aarch64/raspberrypi/dma/raspberrypi-dma.c: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662#note_129009

 > +
 > +#include <bsp/raspberrypi-dma.h>
 > +#define CB_ALIGNMENT 32

There is already an `CPU_CACHE_LINE_BYTES` define for that in RTEMS. Please use that.

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Christian Mauderer started a new discussion on bsps/aarch64/raspberrypi/dma/raspberrypi-dma.c: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662#note_129010

 > +#define CB_ALIGNMENT 32
 > +#define SIZE 16
 > +#define BUFFER_SIZE 64

`SIZE` and `BUFFER_SIZE` seem to be unused.

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Christian Mauderer commented on a discussion on bsps/aarch64/raspberrypi/dma/raspberrypi-dma.c: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662#note_129011

 > +
 > +
 > +void *rpi_unaligned_mem_to_mem_dma( rpi_dma_channel channel, void *src, uint32_t length )

I agree with Kinsey. Either you should remove the function or you should give the user the possibility to pass a destination.


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View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/662
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