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SubjectRe: [PATCH 09/12] i2c: qup: fix buffer overflow for multiple msg of maximum xfer len
On 2018-02-28 03:36, Christ, Austin wrote:
> Hey Abhishek,
>
>
> On 2/3/2018 12:58 AM, Abhishek Sahu wrote:
>> The BAM mode requires buffer for start tag data and tx, rx SG
>> list. Currently, this is being taken for maximum transfer length
>> (65K). But an I2C transfer can have multiple messages and each
>> message can be of this maximum length so the buffer overflow will
>> happen in this case. Since increasing buffer length won’t be
>> feasible since an I2C transfer can contain any number of messages
>> so this patch does following changes to make i2c transfers working
>> for multiple messages case.
>>
>> 1. Calculate the required buffers for 2 maximum length messages
>> (65K * 2).
>> 2. Split the descriptor formation and descriptor scheduling.
>> The idea is to fit as many messages in one DMA transfers for 65K
>> threshold value (max_xfer_sg_len). Whenever the sg_cnt is
>> crossing this, then schedule the BAM transfer and subsequent
>> transfer will again start from zero.
>>

<snip>

>> @@ -1603,7 +1640,7 @@ static int qup_i2c_probe(struct platform_device
>> *pdev)
>> one_bit_t = (USEC_PER_SEC / clk_freq) + 1;
>> qup->one_byte_t = one_bit_t * 9;
>> qup->xfer_timeout = TOUT_MIN * HZ +
>> - usecs_to_jiffies(MX_TX_RX_LEN * qup->one_byte_t);
>> + usecs_to_jiffies(2 * MX_TX_RX_LEN * qup->one_byte_t);
>
> Maybe it would make sense to add a comment here explaining why the
> magic number 2 has been added.

Thanks Austin for reviewing the patches.

Now in v2, I have used the new macro MX_DMA_TX_RX_LEN which will make
this multiplication by 2 more clear. This 2 is for allocating memory
by taking 2 maximum length messages.

https://lkml.org/lkml/2018/3/12/423

Thanks,
Abhishek

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