Re: [PATCH 4/7] misc: Add driver for DAB IP found on Renesas R-Car devices

[Arnd Bergmann <arnd@kernel.org>]

On Thu, Feb 25, 2021 at 11:51 PM Fabrizio Castro
<fabrizio.castro.jz@renesas.com> wrote:
>
> The DAB hardware accelerator found on R-Car E3 and R-Car M3-N devices is
> a hardware accelerator for software DAB demodulators.
> It consists of one FFT (Fast Fourier Transform) module and one decoder
> module, compatible with DAB specification (ETSI EN 300 401 and
> ETSI TS 102 563).
> The decoder module can perform FIC decoding and MSC decoding processing
> from de-puncture to final decoded result.
>
> This patch adds a device driver to support the FFT module only.
>
> Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@renesas.com>
> ---
>  MAINTAINERS                      |   7 ++
>  drivers/misc/Kconfig             |   1 +
>  drivers/misc/Makefile            |   1 +
>  drivers/misc/rcar_dab/Kconfig    |  11 ++
>  drivers/misc/rcar_dab/Makefile   |   8 ++
>  drivers/misc/rcar_dab/rcar_dev.c | 176 +++++++++++++++++++++++++++++++
>  drivers/misc/rcar_dab/rcar_dev.h | 116 ++++++++++++++++++++
>  drivers/misc/rcar_dab/rcar_fft.c | 160 ++++++++++++++++++++++++++++
>  include/uapi/linux/rcar_dab.h    |  35 ++++++

Can you explain why this is not in drivers/media/?

I don't think we want a custom ioctl interface for a device that implements
a generic specification. My first feeling would be that this should not
have a user-level API but instead get called by the DAB radio driver.

What is the intended usage model here? I assume the idea is to
use it in an application that receives audio or metadata from DAB.
What driver do you use for that?

> +static long rcar_dab_unlocked_ioctl(struct file *file, unsigned int cmd,
> +                                   unsigned long arg)
> +{
> +       void __user *argp = (void __user *)arg;
> +       struct rcar_dab *dab;
> +       int ret;
> +
> +       dab = container_of(file->private_data, struct rcar_dab, misc);
> +
> +       switch (cmd) {
> +       case RCAR_DAB_IOC_FFT:
> +               if (!access_ok(argp, sizeof(struct rcar_dab_fft_req)))
> +                       return -EFAULT;
> +               ret = rcar_dab_fft(dab, argp);
> +               break;
> +       default:
> +               ret = -ENOTTY;
> +       }
> +
> +       return ret;
> +}
> +
> +static const struct file_operations rcar_dab_fops = {
> +       .owner          = THIS_MODULE,
> +       .unlocked_ioctl = rcar_dab_unlocked_ioctl,
> +};

There should be a '.compat_ioctl = compat_ptr_ioctl'
entry, provided that the arguments are compatible between
32-bit and 64-bit user space.

> +
> +static int rcar_dab_fft_init(struct rcar_dab *dab, struct rcar_dab_fft_req *fft)
> +{
> +       u32 mode;
> +
> +       for (mode = 0; mode < ARRAY_SIZE(rcar_dab_fft_size_lut); mode++)
> +               if (rcar_dab_fft_size_lut[mode] == fft->points)
> +                       break;
> +       if (mode == ARRAY_SIZE(rcar_dab_fft_size_lut))
> +               return -EINVAL;
> +       if (fft->ofdm_number == 0)
> +               return -EINVAL;
> +
> +       rcar_dab_write(dab, RCAR_DAB_FFTSSR, mode);
> +       rcar_dab_write(dab, RCAR_DAB_FFTNUMOFDMR, fft->ofdm_number);
> +       rcar_dab_write(dab, RCAR_DAB_FFTINADDR, (u32)dab->fft.dma_input_buf);
> +       rcar_dab_write(dab, RCAR_DAB_FFTOUTADDR, (u32)dab->fft.dma_output_buf);

Maybe use lower_32_bits() instead of the (u32) cast.

For clarity, you may also want to specifically ask for a 32-bit DMA mask
in the probe function, with a comment that describes what the hardware
limitation is.

> +
> +       if (copy_from_user(dab->fft.input_buffer, fft_req->input_address,
> +                          buffer_size)) {
> +               mutex_unlock(&dab->fft.lock);
> +               return -EFAULT;
> +       }
> +
> +       dab->fft.done = false;
> +       ret = rcar_dab_fft_init(dab, fft_req);
> +       if (ret) {
> +               mutex_unlock(&dab->fft.lock);
> +               return ret;
> +       }
> +
> +       rcar_dab_fft_enable(dab);
> +       wait_event_interruptible_timeout(dab->fft.wait, dab->fft.done, HZ);
> +       if (!dab->fft.done) {
> +               rcar_dab_fft_disable(dab);
> +               ret = -EFAULT;

-EFAULT doesn't look like the right error for timeout or signal
handling. Better check the return code from wait_event_interruptible_timeout()
instead.

> +
> +struct rcar_dab_fft_req {
> +       int points;                     /*
> +                                        * The number of points to use.
> +                                        * Legal values are 256, 512, 1024, and
> +                                        * 2048.
> +                                        */
> +       unsigned char ofdm_number;      /*
> +                                        * Orthogonal Frequency Division
> +                                        * Multiplexing (OFDM).
> +                                        * Minimum value is 1, maximum value is
> +                                        * 255.
> +                                        */
> +       void __user *input_address;     /*
> +                                        * User space address for the input
> +                                        * buffer.
> +                                        */
> +       void __user *output_address;    /*
> +                                        * User space address for the output
> +                                        * buffer.
> +                                        */
> +};

Please read Documentation/driver-api/ioctl.rst and make this a portable
data structure.

      Arnd