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 12:04:13 +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 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.

> val = YYYY_SET(val, 0x1);          /* set bit 1 - assuming YYYY set
> bit 1 only */
> val = ZZZZ_SET(val, 0x5);            /* set upper 16 bit of the
> register to 0x5 - assuming ZZZZ set field of the upper 16 bits */
>
> Instead writing the above, I am replacing the above 4 lines with these
> two lines:
>
> cmd = CFG_IND_WR_CMD_MASK | CFG_IND_CMD_DONE_MASK;
> cmd = CFG_IND_ADDR_SET(cmd, addr);
>
> Is there clear?
>
> -Loc
>

Cheers
Kishon

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