[U-Boot] [Patch V5 2/4] spi: fsl_qspi: Fix qspi_op_rdid memcpy issue

[york sun]

On 01/22/2016 07:43 AM, Scott Wood wrote:
> On 01/21/2016 09:35 PM, Qianyu Gong wrote:
>>
>>> -----Original Message-----
>>> From: Scott Wood
>>> Sent: Friday, January 22, 2016 3:30 AM
>>> To: Qianyu Gong <qianyu.gong at nxp.com>; u-boot at lists.denx.de;
>>> R58495 at freescale.com
>>> Cc: Mingkai.Hu at freescale.com; jteki at openedev.com; B48286 at freescale.com;
>>> Shaohui.Xie at freescale.com; Wenbin.Song at freescale.com; Scott Wood
>>> <oss at buserror.net>; Gong Qianyu <Qianyu.Gong at freescale.com>
>>> Subject: Re: [Patch V5 2/4] spi: fsl_qspi: Fix qspi_op_rdid memcpy issue
>>>
>>> On 01/20/2016 09:43 PM, Gong Qianyu wrote:
>>>> From: Gong Qianyu <Qianyu.Gong at freescale.com>
>>>>
>>>> In current driver everytime we memcpy 4 bytes to the dest memory
>>>> regardless of the remaining length.
>>>> This patch adds checking the remaining length before memcpy.
>>>> If the length is shorter than 4 bytes, memcpy the actual length of
>>>> data to the dest memory.
>>>>
>>>> Signed-off-by: Gong Qianyu <Qianyu.Gong at freescale.com>
>>>> ---
>>>> V2-V5:
>>>>  - No change.
>>>>
>>>>  drivers/spi/fsl_qspi.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/spi/fsl_qspi.c b/drivers/spi/fsl_qspi.c index
>>>> 38e5900..f178857 100644
>>>> --- a/drivers/spi/fsl_qspi.c
>>>> +++ b/drivers/spi/fsl_qspi.c
>>>> @@ -500,7 +500,10 @@ static void qspi_op_rdid(struct fsl_qspi_priv *priv, u32
>>> *rxbuf, u32 len)
>>>>  		if (rbsr_reg & QSPI_RBSR_RDBFL_MASK) {
>>>>  			data = qspi_read32(priv->flags, &regs->rbdr[i]);
>>>>  			data = qspi_endian_xchg(data);
>>>> -			memcpy(rxbuf, &data, 4);
>>>> +			if (size < 4)
>>>> +				memcpy(rxbuf, &data, size);
>>>> +			else
>>>> +				memcpy(rxbuf, &data, 4);
>>>
>>> memcpy(rxbuf, &data, min(size, 4));
>>>
>>>>  			rxbuf++;
>>>>  			size -= 4;
>>>>  			i++;
>>>
>>> size -= 4 even if size was < 4?
>>>
>>> -Scott
>>
>> Yes.. The following is complete code:
>>
>>         i = 0;
>>         size = len;
>>         while ((RX_BUFFER_SIZE >= size) && (size > 0)) {
>>                 rbsr_reg = qspi_read32(priv->flags, &regs->rbsr);
>>                 if (rbsr_reg & QSPI_RBSR_RDBFL_MASK) {
>>                         data = qspi_read32(priv->flags, &regs->rbdr[i]);
>>                         data = qspi_endian_xchg(data);
>>                         memcpy(rxbuf, &data, min(size, 4));
>>                         rxbuf++;
>>                         size -= 4;
>>                         i++;
>>                 }
>>         }
> 
> I'm not saying it doesn't work (assuming i is signed, which the
> "complete code" above doesn't show).  I'm saying it looks weird, and it
> would be better to have a variable that holds min(size, 4) and pass that
> to both memcpy and the subtraction.
> 

Qianyu,

Previously I said it looked weird for doing this. Please fix.

"size" is declared as "int".
"len" is declared as u32. That's not "int". If you trace back the functions, you
may see it came from DIV_ROUND_UP(bitlen, 8) where bitlen is "unsigned int". So
technically the code is safe. But it is _confusing_. We don't want to confuse
ourselves when reading the code later. And the fix is easy, isn't it?

York