linux-kernel - Re: [PATCH RESEND v10 3/4] PHY: add APM X-Gene SoC 15Gbps Multi-purpose PHY driver

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Date:	Thu, 27 Feb 2014 12:12:09 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Loc Ho <lho@....com>
CC:	Tejun Heo <tj@...nel.org>, Olof Johansson <olof@...om.net>,
	Arnd Bergmann <arnd@...db.de>, <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Don Dutile <ddutile@...hat.com>, Jon Masters <jcm@...hat.com>,
	"patches@....com" <patches@....com>, Tuan Phan <tphan@....com>,
	Suman Tripathi <stripathi@....com>
Subject: Re: [PATCH RESEND v10 3/4] PHY: add APM X-Gene SoC 15Gbps Multi-purpose
 PHY driver

On Thursday 27 February 2014 12:04 PM, Kishon Vijay Abraham I wrote:
> On Thursday 27 February 2014 11:55 AM, Loc Ho wrote:
>> Hi,
>>
>>>>>> +
>>>>>> +static void sds_wr(void __iomem *csr_base, u32 indirect_cmd_reg,
>>>>>> +                  u32 indirect_data_reg, u32 addr, u32 data)
>>>>>> +{
>>>>>> +       u32 val;
>>>>>> +       u32 cmd;
>>>>>> +
>>>>>> +       cmd = CFG_IND_WR_CMD_MASK | CFG_IND_CMD_DONE_MASK;
>>>>>> +       cmd = CFG_IND_ADDR_SET(cmd, addr);
>>>>>
>>>>>
>>>>>
>>>>> This looks hacky. If 'CFG_IND_WR_CMD_MASK | CFG_IND_CMD_DONE_MASK'
>>>>> should
>>>>> be set then it should be part of the second argument. From the macro
>>>>> 'CFG_IND_ADDR_SET' the first argument should be more like the
>>>>> current value
>>>>> present in the register right? I feel the macro (CFG_IND_ADDR_SET)
>>>>> is not
>>>>> used in the way it is intended to.
>>>>
>>>>
>>>> The macro XXX_SET is intended to update an field within the register.
>>>> The update field is returned. The first assignment lines are setting
>>>> another field. Those two lines can be written as:
>>>>
>>>> cmd = 0;
>>>> cmd |= CFG_IND_WR_CMD_MASK;            ==> Set the CMD bit
>>>> cmd |= CFG_IND_CMD_DONE_MASK;        ==> Set the DONE bit
>>>> cmd = CFG_IND_ADDR_SET(cmd, addr);    ===> Set the field ADDR
>>>
>>>
>>> #define  CFG_IND_ADDR_SET(dst, src) \
>>>                  (((dst) & ~0x003ffff0) | (((u32)(src)<<4) &
>>> 0x003ffff0))
>>>
>>>  From this macro the first argument should be the present value in that
>>> register. Here you reset the address bits and write the new address
>>> bits.
>>
>> Yes.. This is correct. I am clearing x number of bit and then set new
>> value.
>>
>>> IMO the first argument should be the value in 'csr_base +
>>> indirect_cmd_reg'.
>>> So it resets the address bits in 'csr_base + indirect_cmd_reg' and write
>>> down the new address bits.
>>
>> Yes.. The above code does just that. In addition, I am also setting
>> the bits CFG_IND_WR_CMD_MASK and CFG_IND_CMD_DONE_MASK with the two
>> previous statement. Think of the code flow as follow:
>>
>> val = readl(some void * address); /* read the register */
>
> Where are you reading the register in your code (before CFG_IND_ADDR_SET)?
>> val = XXXX_SET(val, 0x1);            /* set bit 0  - assuming XXXX set
>> bit 0 only */
> If you want to set other bits (other than address) don't use
> CFG_IND_ADDR_SET macro. That looks hacky to me.

huh.. looked it again and I think only the readl is missing. If you can 
add that, it should be fine.

How about something like this

val = readl(csr_base + indirect_cmd_reg);
val = CFG_IND_ADDR_SET(val, addr);
val |= CFG_IND_WR_CMD_MASK | CFG_IND_CMD_DONE_MASK;
writel(val, csr_base + indirect_cmd_reg);

Cheers
Kishon
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