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Groups > comp.os.linux.development.system > #213

Re: mmap dma buffer

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On Jul 8, 12:01 pm, Pavel Borzenkov <pa...@devio.us> wrote:
> On 2011-07-07, new <luvra...@gmail.com> wrote:
>
> > okay.. the mmap_buf is filled with data and passed to write() call,the
> > write callback in driver creates the descriptor chain and initiates
> > the DMA engine.
>
> If you are using mmap, don't use write to trigger DMA (it's very confusing).
> Better style is to add new ioctl for this:
>
> buf = mmap(....);
> memcpy(buf, <data to be written to device>, <data size>);
> ioctl(fd, START_DMA_WRITE, <data size>);
>
> > Now to verify if the data is written properly to the device, i need to
> > read the data, this is where i'm a bit struck. For reading the data,
> > do I need to mmap and call read() function? where the read callback in
> > driver will create the descriptor chain and initiate the DMA.
> > Is this the correct way to read the data?
>
> You don't need to do mmap again, the buffer is already mapped to the process'
> address space. You may verify the data like this:
>
> memset(buf, 0, <buf size>); /* required to verify that we actually read
>                                something from the device */
> ioctl(fd, START_DMA_READ, <data size>);
>
> After that you can compare data like this:
> memcmp(buf, <data that was written to device>, <data size>);
>
> You may want to add 'poll' support into your driver to notify userspace process
> that DMA read/write has completed.
>
> --
> Pavel

Oh okay... Thanks a lot Pavel.
Really Appreciate. Will get back with the updated code.

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Thread

mmap dma buffer new <luvraghu@gmail.com> - 2011-07-06 08:12 -0700
  Re: mmap dma buffer Pavel Borzenkov <pavel@devio.us> - 2011-07-07 09:59 +0000
    Re: mmap dma buffer Pavel Borzenkov <pavel@devio.us> - 2011-07-07 10:02 +0000
      Re: mmap dma buffer new <luvraghu@gmail.com> - 2011-07-07 05:42 -0700
        Re: mmap dma buffer Pavel Borzenkov <pavel@devio.us> - 2011-07-07 13:27 +0000
          Re: mmap dma buffer new <luvraghu@gmail.com> - 2011-07-07 07:46 -0700
            Re: mmap dma buffer Pavel Borzenkov <pavel@devio.us> - 2011-07-08 07:01 +0000
              Re: mmap dma buffer new <luvraghu@gmail.com> - 2011-07-08 03:31 -0700

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