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

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Date:	Wed, 26 Feb 2014 22:25:25 -0800
From:	Loc Ho <lho@....com>
To:	Kishon Vijay Abraham I <kishon@...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

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 */
val = XXXX_SET(val, 0x1);            /* set bit 0  - assuming XXXX set
bit 0 only */
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
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