Re: [PATCH v2 05/11] PCI/VGA: Move the new_state assignment out of the loop

Ilpo Järvinen
2023-08-09T13:55:46Z

On Wed, 9 Aug 2023, Sui Jingfeng wrote:

> From: Sui Jingfeng <suijingfeng@loongson.cn>
>
> In the vga_arbiter_notify_clients() function, the value of the 'new_state'
> variable will be 'false' on systems that have more than one VGA device.
> The value will be 'true' if there is only one VGA device or no VGA device
> at all. Hence, its value is not relevant to the iteration of the loop.
>
> So move the assignment clause out of the loop. For a system with multiple
> video cards, this patch saves unnecessary assignment.
>
> Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
> ---
> drivers/pci/vgaarb.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> index dc10a262fb5e..6883067a802a 100644
> --- a/drivers/pci/vgaarb.c
> +++ b/drivers/pci/vgaarb.c
> @@ -1468,22 +1468,20 @@ static void vga_arbiter_notify_clients(void)
> {
> struct vga_device *vgadev;
> unsigned long flags;
> - uint32_t new_decodes;
> - bool new_state;
> + bool state;
>
> if (!vga_arbiter_used)
> return;
>
> + state = (vga_count > 1) ? false : true;
> +

Is it safe to move this outside of the lock?

This would be enough (no need for ?: construct):

state = vga_count <= 1;

Or if you want to keep it as > 1:

state = !(vga_count > 1);

> spin_lock_irqsave(&vga_lock, flags);
> list_for_each_entry(vgadev, &vga_list, list) {
> - if (vga_count > 1)
> - new_state = false;
> - else
> - new_state = true;
> if (vgadev->set_decode) {
> - new_decodes = vgadev->set_decode(vgadev->pdev,
> - new_state);
> - vga_update_device_decodes(vgadev, new_decodes);
> + unsigned int decodes;
> +
> + decodes = vgadev->set_decode(vgadev->pdev, state);
> + vga_update_device_decodes(vgadev, decodes);
> }
> }
> spin_unlock_irqrestore(&vga_lock, flags);
>

--
i.