linux-kernel - Re: [PATCH v7 5/7] drm: bridge/dw-hdmi: add support for multi byte register width access

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Date:	Tue, 11 Nov 2014 14:37:47 +0000
From:	Zubair Lutfullah Kakakhel <Zubair.Kakakhel@...tec.com>
To:	Lucas Stach <l.stach@...gutronix.de>
CC:	Andy Yan <andy.yan@...k-chips.com>, <airlied@...ux.ie>,
	<heiko@...ech.de>, <fabio.estevam@...escale.com>,
	<rmk+kernel@....linux.org.uk>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Shawn Guo <shawn.guo@...aro.org>,
	Josh Boyer <jwboyer@...hat.com>,
	Sean Paul <seanpaul@...omium.org>,
	Inki Dae <inki.dae@...sung.com>,
	Dave Airlie <airlied@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, <djkurtz@...gle.com>,
	<ykk@...k-chips.com>, <linux-kernel@...r.kernel.org>,
	<dri-devel@...ts.freedesktop.org>, <devel@...verdev.osuosl.org>,
	<devicetree@...r.kernel.org>, <linux-rockchip@...ts.infradead.org>,
	<jay.xu@...k-chips.com>
Subject: Re: [PATCH v7 5/7] drm: bridge/dw-hdmi: add support for multi byte
 register width access



On 11/11/14 14:23, Lucas Stach wrote:
> Am Dienstag, den 11.11.2014, 14:20 +0000 schrieb Zubair Lutfullah
> Kakakhel:
>> Hi Andy,
>>
>> This patch adds the reg-io-width binding.
>>
>> Hence the binding patch should come before it.
>>
>>
>> On 11/11/14 12:53, Andy Yan wrote:
>>> On rockchip rk3288, only word(32-bit) accesses are
>>> permitted for hdmi registers.  Byte width accesses (writeb,
>>> readb) generate an imprecise external abort.
>>>
>>> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
>>>
>>> ---
>>>
>>>  }
>>>  
>>>  static void hdmi_modb(struct dw_hdmi *hdmi, u8 data, u8 mask, unsigned reg)
>>> @@ -1499,6 +1527,23 @@ static int dw_hdmi_bind(struct device *dev, struct device *master, void *data)
>>>  	struct device_node *ddc_node;
>>>  	struct resource *iores;
>>>  	int ret, irq;
>>> +	u32 val = 1;
>>> +
>>> +	of_property_read_u32(np, "reg-io-width", &val);
>>> +
>>> +	switch (val) {
>>> +	case 4:
>>> +		hdmi->write = dw_hdmi_writel;
>>> +		hdmi->read = dw_hdmi_readl;
>>> +		break;
>>> +	case 1:
>>> +		hdmi->write = dw_hdmi_writeb;
>>> +		hdmi->read = dw_hdmi_readb;
>>> +		break;
>>> +	default:
>>> +		dev_err(dev, "reg-io-width must be 1 or 4\n");
>>> +		return -EINVAL;
>>> +	}
>>
>> The binding patch says this is an optional property.
>> But here if undefined it returns -EINVAL.
>>
>> I would keep it optional and default it to byte access.
> 
> That's exactly what the patch does. val is initialized to 1, which is
> not changed if the property could not be found in the DT. The default
> case will only be taken if the property is present in DT but has any
> other value than 1 or 4, which is an error.
> 

I missed the initialization. My bad.

Thanks
ZubairLK
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