[linuxdc-dev]Dreamcast sound and kernel memory

[Adrian M. <ad...@mc...>]

Well, maybe I should be writing ARM code after all - but I'm still going to 
give the SH4 stuff one more try and I have a question which I wonder if 
someone might help me with.

In the dsp write the code currently does this...

static ssize_t aica_audio_do_write(struct file *file,
				   const char *buffer,
				   size_t count,
				   loff_t *ppos)
{
  
  aica_dev_t *devc=file->private_data;

  //really want to write?
  if (!(file->f_mode & FMODE_WRITE)) return -EINVAL;
  

  //now output this to the selected channel

  //fill a chunk of the sound memory with the contents of the buffer
  aica_halt_channel(devc->channel); //halt anything playing there already
  int offset = 0xf000;
  if (copy_from_user((void*)(0xa0800000 + offset), (const void*) buffer, 
count))
    {
      DEBGM("Failed to copy memory bufferfrom user space\n");
      return -EFAULT;
    }

.
.
.
.
...........Lots of code..........
.

   
  return count;

}

Now, is it right to just copy a lump of memory over from user space in this 
way?

I haven't specifically allocated a buffer inside the sound RAM area - just 
claimed it for the kernel when initiating the module and assumed that it's 
there - the function doesn't fail in the sense that the -EFAULT error is 
never reported, but does that mean it has actually worked?

Should I be allocating a buffer first and copying the data from user space 
into that?

Perhaps I am just clutching at straws.