linux-kernel - Re: [PATCH] usb: gadget: aspeed: fixup vhub port irq handling

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Date:   Mon, 17 Aug 2020 16:49:32 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     rentao.bupt@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Stephen Boyd <swboyd@...omium.org>, linux-usb@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        openbmc@...ts.ozlabs.org, taoren@...com
Cc:     Tao Ren <rentao.bupt@...il.com>
Subject: Re: [PATCH] usb: gadget: aspeed: fixup vhub port irq handling


Hi,

rentao.bupt@...il.com writes:
> From: Tao Ren <rentao.bupt@...il.com>
>
> This is a follow-on patch for commit a23be4ed8f48 ("usb: gadget: aspeed:
> improve vhub port irq handling"): for_each_set_bit() is replaced with
> simple for() loop because for() loop runs faster on ASPEED BMC.
>
> Signed-off-by: Tao Ren <rentao.bupt@...il.com>
> ---
>  drivers/usb/gadget/udc/aspeed-vhub/core.c | 10 +++-------
>  drivers/usb/gadget/udc/aspeed-vhub/vhub.h |  3 +++
>  2 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/aspeed-vhub/core.c b/drivers/usb/gadget/udc/aspeed-vhub/core.c
> index cdf96911e4b1..be7bb64e3594 100644
> --- a/drivers/usb/gadget/udc/aspeed-vhub/core.c
> +++ b/drivers/usb/gadget/udc/aspeed-vhub/core.c
> @@ -135,13 +135,9 @@ static irqreturn_t ast_vhub_irq(int irq, void *data)
>  
>  	/* Handle device interrupts */
>  	if (istat & vhub->port_irq_mask) {
> -		unsigned long bitmap = istat;
> -		int offset = VHUB_IRQ_DEV1_BIT;
> -		int size = VHUB_IRQ_DEV1_BIT + vhub->max_ports;
> -
> -		for_each_set_bit_from(offset, &bitmap, size) {
> -			i = offset - VHUB_IRQ_DEV1_BIT;
> -			ast_vhub_dev_irq(&vhub->ports[i].dev);
> +		for (i = 0; i < vhub->max_ports; i++) {
> +			if (istat & VHUB_DEV_IRQ(i))
> +				ast_vhub_dev_irq(&vhub->ports[i].dev);

how have you measured your statement above? for_each_set_bit() does
exactly what you did. Unless your architecture has an instruction which
helps finds the next set bit (like cls on ARM), which, then, makes it
much faster.

-- 
balbi

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