linux-kernel - Re: [PATCH v17 4/8] drm: bridge: Cadence: Add MHDP8501 DP/HDMI driver

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Message-ID: <2mug3ii2vi735sk7nwwu2rcj63d3mlgazlhg4sydcxb6uf5nsc@qi5ut5pmajsv>
Date: Tue, 24 Sep 2024 16:47:45 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Sandor Yu <Sandor.yu@....com>, andrzej.hajda@...el.com, 
	neil.armstrong@...aro.org, Laurent.pinchart@...asonboard.com, jonas@...boo.se, 
	jernej.skrabec@...il.com, airlied@...il.com, daniel@...ll.ch, robh+dt@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org, s.hauer@...gutronix.de, festevam@...il.com, 
	vkoul@...nel.org, dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org, 
	kernel@...gutronix.de, linux-imx@....com, oliver.brown@....com, 
	alexander.stein@...tq-group.com, sam@...nborg.org
Subject: Re: [PATCH v17 4/8] drm: bridge: Cadence: Add MHDP8501 DP/HDMI driver

On Tue, Sep 24, 2024 at 12:16:27PM GMT, Maxime Ripard wrote:
> On Tue, Sep 24, 2024 at 03:36:49PM GMT, Sandor Yu wrote:
> > +static int cdns_mhdp8501_read_hpd(struct cdns_mhdp8501_device *mhdp)
> > +{
> > +	u8 status;
> > +	int ret;
> > +
> > +	mutex_lock(&mhdp_mailbox_mutex);
> > +
> > +	ret = cdns_mhdp_mailbox_send(&mhdp->base, MB_MODULE_ID_GENERAL,
> > +				     GENERAL_GET_HPD_STATE, 0, NULL);
> > +	if (ret)
> > +		goto err_get_hpd;
> > +
> > +	ret = cdns_mhdp_mailbox_recv_header(&mhdp->base, MB_MODULE_ID_GENERAL,
> > +					    GENERAL_GET_HPD_STATE,
> > +					    sizeof(status));
> > +	if (ret)
> > +		goto err_get_hpd;
> > +
> > +	ret = cdns_mhdp_mailbox_recv_data(&mhdp->base, &status, sizeof(status));
> > +	if (ret)
> > +		goto err_get_hpd;
> > +
> > +	mutex_unlock(&mhdp_mailbox_mutex);
> 
> That's better I guess, but it's still not a good API design. If you
> can't have concurrent accesses, then cdns_mhdp_mailbox_send et al.
> should take the mutex themselves.

I think that a proper API might be:

int cdns_mhdp_mailbox_send_recv(struct cdns_mhdp_device *mhdp,
			u8 module_id, u8 opcode,
			u16 size, const u8 *message,
			u16 buf_size, u8 *buf);

Internally it should take the lock, exchange the data, then return.

-- 
With best wishes
Dmitry