Re: [PATCH v3 02/11] esp: rework write_response() to avoid using the FIFO for DMA transactions

[Philippe Mathieu-Daudé]

On 4/1/21 9:49 AM, Mark Cave-Ayland wrote:
> The code for write_response() has always used the FIFO to store the data for
> the status/message in phases, even for DMA transactions. Switch to using a
> separate buffer that can be used directly for DMA transactions and restrict
> the FIFO use to the non-DMA case.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
> ---
>  hw/scsi/esp.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c
> index bafea0d4e6..26fe1dcb9d 100644
> --- a/hw/scsi/esp.c
> +++ b/hw/scsi/esp.c
> @@ -445,18 +445,16 @@ static void write_response_pdma_cb(ESPState *s)
>  
>  static void write_response(ESPState *s)
>  {
> -    uint32_t n;
> +    uint8_t buf[2];
>  
>      trace_esp_write_response(s->status);
>  
> -    fifo8_reset(&s->fifo);
> -    esp_fifo_push(s, s->status);
> -    esp_fifo_push(s, 0);
> +    buf[0] = s->status;
> +    buf[1] = 0;

Slightly simplified:

       const uint8_t buf[2] = { s->status, 0 };

>      if (s->dma) {

           uint32_t n;

>          if (s->dma_memory_write) {
> -            s->dma_memory_write(s->dma_opaque,
> -                                (uint8_t *)fifo8_pop_buf(&s->fifo, 2, &n), 
> 2);
> +            s->dma_memory_write(s->dma_opaque, buf, 2);
>              s->rregs[ESP_RSTAT] = STAT_TC | STAT_ST;
>              s->rregs[ESP_RINTR] |= INTR_BS | INTR_FC;
>              s->rregs[ESP_RSEQ] = SEQ_CD;
> @@ -466,7 +464,8 @@ static void write_response(ESPState *s)
>              return;
>          }
>      } else {
> -        s->ti_size = 2;
> +        fifo8_reset(&s->fifo);
> +        fifo8_push_all(&s->fifo, buf, 2);
>          s->rregs[ESP_RFLAGS] = 2;
>      }
>      esp_raise_irq(s);
> 

Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org>