Re: [PATCH v3 09/16] gpu: host1x: Optimize CDMA push buffer memory usage

[Dmitry Osipenko <digetx@gmail.com>]

01.02.2019 16:28, Thierry Reding пишет:
> From: Thierry Reding <treding@nvidia.com>
> 
> The host1x CDMA push buffer is terminated by a special opcode (RESTART)
> that tells the CDMA to wrap around to the beginning of the push buffer.
> To accomodate the RESTART opcode, an extra 4 bytes are allocated on top
> of the 512 * 8 = 4096 bytes needed for the 512 slots (1 slot = 2 words)
> that are used for other commands passed to CDMA. This requires that two
> memory pages are allocated, but most of the second page (4092 bytes) is
> never used.
> 
> Decrease the number of slots to 511 so that the RESTART opcode fits
> within the page. Adjust the push buffer wraparound code to take into
> account push buffer sizes that are not a power of two.
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/host1x/cdma.c | 29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/host1x/cdma.c b/drivers/gpu/host1x/cdma.c
> index a96c4dd1e449..50c1370b56c7 100644
> --- a/drivers/gpu/host1x/cdma.c
> +++ b/drivers/gpu/host1x/cdma.c
> @@ -42,7 +42,17 @@
>   * means that the push buffer is full, not empty.
>   */
>  
> -#define HOST1X_PUSHBUFFER_SLOTS	512
> +/*
> + * Typically the commands written into the push buffer are a pair of words. We
> + * use slots to represent each of these pairs and to simplify things. Note the
> + * strange number of slots allocated here. 512 slots will fit exactly within a
> + * single memory page. We also need one additional word at the end of the push
> + * buffer for the RESTART opcode that will instruct the CDMA to jump back to
> + * the beginning of the push buffer. With 512 slots, this means that we'll use
> + * 2 memory pages and waste 4092 bytes of the second page that will never be
> + * used.
> + */
> +#define HOST1X_PUSHBUFFER_SLOTS	511
>  
>  /*
>   * Clean up push buffer resources
> @@ -148,7 +158,10 @@ static void host1x_pushbuffer_push(struct push_buffer *pb, u32 op1, u32 op2)
>  	WARN_ON(pb->pos == pb->fence);
>  	*(p++) = op1;
>  	*(p++) = op2;
> -	pb->pos = (pb->pos + 8) & (pb->size - 1);
> +	pb->pos += 8;
> +
> +	if (pb->pos >= pb->size)
> +		pb->pos -= pb->size;
>  }
>  
>  /*
> @@ -158,7 +171,10 @@ static void host1x_pushbuffer_push(struct push_buffer *pb, u32 op1, u32 op2)
>  static void host1x_pushbuffer_pop(struct push_buffer *pb, unsigned int slots)
>  {
>  	/* Advance the next write position */
> -	pb->fence = (pb->fence + slots * 8) & (pb->size - 1);
> +	pb->fence += slots * 8;
> +
> +	if (pb->fence >= pb->size)
> +		pb->fence -= pb->size;
>  }
>  
>  /*
> @@ -166,7 +182,12 @@ static void host1x_pushbuffer_pop(struct push_buffer *pb, unsigned int slots)
>   */
>  static u32 host1x_pushbuffer_space(struct push_buffer *pb)
>  {
> -	return ((pb->fence - pb->pos) & (pb->size - 1)) / 8;
> +	unsigned int fence = pb->fence;
> +
> +	if (pb->fence < pb->pos)
> +		fence += pb->size;
> +
> +	return (fence - pb->pos) / 8;
>  }
>  
>  /*
> 

Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
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