linux-kernel - Re: [PATCH] virtio-mmio: read[wl]()/write[wl] are already little-endian

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Date:   Thu, 11 Mar 2021 10:44:47 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Laurent Vivier <laurent@...ier.eu>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH] virtio-mmio: read[wl]()/write[wl] are already
 little-endian

On Tue, Mar 09, 2021 at 11:43:13PM +0100, Laurent Vivier wrote:
> read[wl]()/write[wl] already access memory in little-endian mode.

But then they convert it to CPU right? We just convert it back ...

> No need to convert the value with cpu_to_leXX()/leXX_to_cpu()
> 
> Signed-off-by: Laurent Vivier <laurent@...ier.eu>
> ---
>  drivers/virtio/virtio_mmio.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index a286d22b6551..3f6a5588f77d 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -168,17 +168,17 @@ static void vm_get(struct virtio_device *vdev, unsigned offset,
>  		memcpy(buf, &b, sizeof b);
>  		break;
>  	case 2:
> -		w = cpu_to_le16(readw(base + offset));
> +		w = readw(base + offset);
>  		memcpy(buf, &w, sizeof w);
>  		break;
>  	case 4:
> -		l = cpu_to_le32(readl(base + offset));
> +		l = readl(base + offset);
>  		memcpy(buf, &l, sizeof l);
>  		break;
>  	case 8:
> -		l = cpu_to_le32(readl(base + offset));
> +		l = readl(base + offset);
>  		memcpy(buf, &l, sizeof l);
> -		l = cpu_to_le32(ioread32(base + offset + sizeof l));
> +		l = ioread32(base + offset + sizeof l);
>  		memcpy(buf + sizeof l, &l, sizeof l);
>  		break;
>  	default:
> @@ -212,17 +212,17 @@ static void vm_set(struct virtio_device *vdev, unsigned offset,
>  		break;
>  	case 2:
>  		memcpy(&w, buf, sizeof w);
> -		writew(le16_to_cpu(w), base + offset);
> +		writew(w, base + offset);
>  		break;
>  	case 4:
>  		memcpy(&l, buf, sizeof l);
> -		writel(le32_to_cpu(l), base + offset);
> +		writel(l, base + offset);
>  		break;
>  	case 8:
>  		memcpy(&l, buf, sizeof l);
> -		writel(le32_to_cpu(l), base + offset);
> +		writel(l, base + offset);
>  		memcpy(&l, buf + sizeof l, sizeof l);
> -		writel(le32_to_cpu(l), base + offset + sizeof l);
> +		writel(l, base + offset + sizeof l);
>  		break;
>  	default:
>  		BUG();
> -- 
> 2.29.2