Re: [PATCH] [media] s5p-mfc: Align stream buffer and CPB buffer to 512

[Andrzej Hajda]

Hi Smitha,

On 18.01.2017 10:37, Smitha T Murthy wrote:
> >From MFCv6 onwards encoder stream buffer and decoder CPB buffer

Unexpected char at the beginning.

> need to be aligned with 512.

Patch below adds checks only if buffer size is multiple of 512, am I right?
If yes, please precise the subject, for example "...CPB buffer size need
to be...".


>
> Signed-off-by: Smitha T Murthy <smitha.t@xxxxxxxxxxx>
> ---
>  drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.c |    9 +++++++++
>  drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.h |    3 +++
>  2 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.c b/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.c
> index d6f207e..57da798 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.c
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.c
> @@ -408,8 +408,15 @@ static int s5p_mfc_set_dec_stream_buffer_v6(struct s5p_mfc_ctx *ctx,
>  	struct s5p_mfc_dev *dev = ctx->dev;
>  	const struct s5p_mfc_regs *mfc_regs = dev->mfc_regs;
>  	struct s5p_mfc_buf_size *buf_size = dev->variant->buf_size;
> +	size_t cpb_buf_size;
>  
>  	mfc_debug_enter();
> +	cpb_buf_size = ALIGN(buf_size->cpb, CPB_ALIGN);

Since buf_size->cpb is constant of know size there is no need to align
it here.

> +	if (strm_size >= set_strm_size_max(cpb_buf_size)) {
> +		mfc_debug(2, "Decrease strm_size : %u -> %zu, gap : %d\n",
> +			strm_size, set_strm_size_max(cpb_buf_size), CPB_ALIGN);
> +		strm_size = set_strm_size_max(cpb_buf_size);
> +	}

As I understand strm_size here is a size of buffer to be decoded, why it
cannot be equal to buf_size->cpb? Commit message says nothing about it.

>  	mfc_debug(2, "inst_no: %d, buf_addr: 0x%08x,\n"
>  		"buf_size: 0x%08x (%d)\n",
>  		ctx->inst_no, buf_addr, strm_size, strm_size);
> @@ -519,6 +526,8 @@ static int s5p_mfc_set_enc_stream_buffer_v6(struct s5p_mfc_ctx *ctx,
>  	struct s5p_mfc_dev *dev = ctx->dev;
>  	const struct s5p_mfc_regs *mfc_regs = dev->mfc_regs;
>  
> +	size = ALIGN(size, 512);
> +

Shouldn't be CPB_ALIGN instead of 512? And more importantly size is a
length of buffer for encoded stream,
by up-aligning you tell MFC that it can write beyond the buffer, it
could potentially overwrite random memory? Am I right?


>  	writel(addr, mfc_regs->e_stream_buffer_addr); /* 16B align */
>  	writel(size, mfc_regs->e_stream_buffer_size);
>  
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.h b/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.h
> index 8055848..16a7b1d 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.h
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc_opr_v6.h
> @@ -40,6 +40,9 @@
>  #define FRAME_DELTA_H264_H263		1
>  #define TIGHT_CBR_MAX			10
>  
> +#define CPB_ALIGN			512
> +#define set_strm_size_max(cpb_max)	((cpb_max) - CPB_ALIGN)

Name of the macro is misleading.

Regards
Andrzej

> +
>  struct s5p_mfc_hw_ops *s5p_mfc_init_hw_ops_v6(void);
>  const struct s5p_mfc_regs *s5p_mfc_init_regs_v6_plus(struct s5p_mfc_dev *dev);
>  #endif /* S5P_MFC_OPR_V6_H_ */