linux-kernel - Re: [PATCH 1/2] drm/bridge: samsung-dsim: use while loop in samsung_dsim_transfer

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Message-ID: <e76acf6f-2b2b-4b4c-9dd7-b44872081875@kontron.de>
Date: Tue, 27 May 2025 16:52:16 +0200
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: Philipp Zabel <p.zabel@...gutronix.de>, Inki Dae <inki.dae@...sung.com>,
 Jagan Teki <jagan@...rulasolutions.com>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 kernel@...gutronix.de
Subject: Re: [PATCH 1/2] drm/bridge: samsung-dsim: use while loop in
 samsung_dsim_transfer_start

Am 27.05.25 um 16:21 schrieb Philipp Zabel:
> Turn the open-coded goto-again construct into a while loop, to make
> samsung_dsim_transfer_start() a bit shorter and easier to read.
> 
> Hold the spinlock when looping back around and avoid the duplicated
> list_empty() check.
> 
> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>

Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>

> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 51 +++++++++++++++--------------------
>  1 file changed, 21 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 0014c497e3fe7d8349a119dbdda30d65d816cccf..1dfc9710bee5134e0e0114ce52f673c21564b11b 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1235,43 +1235,34 @@ static void samsung_dsim_transfer_start(struct samsung_dsim *dsi)
>  {
>  	unsigned long flags;
>  	struct samsung_dsim_transfer *xfer;
> -	bool start = false;
>  
> -again:
>  	spin_lock_irqsave(&dsi->transfer_lock, flags);
>  
> -	if (list_empty(&dsi->transfer_list)) {
> +	while (!list_empty(&dsi->transfer_list)) {
> +		xfer = list_first_entry(&dsi->transfer_list,
> +					struct samsung_dsim_transfer, list);
> +
>  		spin_unlock_irqrestore(&dsi->transfer_lock, flags);
> -		return;
> +
> +		if (xfer->packet.payload_length &&
> +		    xfer->tx_done == xfer->packet.payload_length)
> +			/* waiting for RX */
> +			return;
> +
> +		samsung_dsim_send_to_fifo(dsi, xfer);
> +
> +		if (xfer->packet.payload_length || xfer->rx_len)
> +			return;
> +
> +		xfer->result = 0;
> +		complete(&xfer->completed);
> +
> +		spin_lock_irqsave(&dsi->transfer_lock, flags);
> +
> +		list_del_init(&xfer->list);
>  	}
>  
> -	xfer = list_first_entry(&dsi->transfer_list,
> -				struct samsung_dsim_transfer, list);
> -
>  	spin_unlock_irqrestore(&dsi->transfer_lock, flags);
> -
> -	if (xfer->packet.payload_length &&
> -	    xfer->tx_done == xfer->packet.payload_length)
> -		/* waiting for RX */
> -		return;
> -
> -	samsung_dsim_send_to_fifo(dsi, xfer);
> -
> -	if (xfer->packet.payload_length || xfer->rx_len)
> -		return;
> -
> -	xfer->result = 0;
> -	complete(&xfer->completed);
> -
> -	spin_lock_irqsave(&dsi->transfer_lock, flags);
> -
> -	list_del_init(&xfer->list);
> -	start = !list_empty(&dsi->transfer_list);
> -
> -	spin_unlock_irqrestore(&dsi->transfer_lock, flags);
> -
> -	if (start)
> -		goto again;
>  }
>  
>  static bool samsung_dsim_transfer_finish(struct samsung_dsim *dsi)
>