Re: [linuxdc-dev]Dreamcast sound and kernel memory

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

On Sunday 02 Dec 2001 4:18 pm, Adrian McMenamin wrote:
> 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.
>


My own tests suggest this to be the case :-<