Re: [PATCH 09/12] i2c: qup: fix buffer overflow for multiple msg of maximum xfer len

[Abhishek Sahu]

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 wonât 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