Messages in this thread | | | Subject | Re: [PATCH v3] i2c: Squash of SMBus block read patchset to save power | From | Jarkko Nikula <> | Date | Wed, 16 Sep 2020 17:09:18 +0300 |
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On 9/15/20 8:48 PM, Sultan Alsawaf wrote: > On Tue, Sep 15, 2020 at 02:55:48PM +0300, Jarkko Nikula wrote: >> I tested this on top of fc4f28bb3daf ("Merge tag 'for-5.9-rc5-tag' of >> git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux") and seems to be >> working fine. What was the key change compared to previous version that was >> regressing for me? > > This change fixed your issue (and my issue with 5.8): > --- a/drivers/i2c/busses/i2c-designware-master.c > +++ b/drivers/i2c/busses/i2c-designware-master.c > @@ -395,8 +395,9 @@ i2c_dw_recv_len(struct dw_i2c_dev *dev, u8 len) > * Adjust the buffer length and mask the flag > * after receiving the first byte. > */ > - len += (flags & I2C_CLIENT_PEC) ? 2 : 1; > - dev->tx_buf_len = len - min_t(u8, len, dev->rx_outstanding); > + if (flags & I2C_CLIENT_PEC) > + len++; > + dev->tx_buf_len = len - min_t(u8, len - 1, dev->rx_outstanding); > msgs[dev->msg_read_idx].len = len; > msgs[dev->msg_read_idx].flags &= ~I2C_M_RECV_LEN; > > I've attributed this change with the following commit message: > "i2c: designware: Ensure tx_buf_len is nonzero for SMBus block reads > > The point of adding a byte to len in i2c_dw_recv_len() is to make sure > that tx_buf_len is nonzero, so that i2c_dw_xfer_msg() can let the i2c > controller know that the i2c transaction can end. Otherwise, the i2c > controller will think that the transaction can never end for block > reads, which results in the stop-detection bit never being set and thus > the transaction timing out. > > Adding a byte to len is not a reliable way to do this though; sometimes > it lets tx_buf_len become zero, which results in the scenario described > above. Therefore, just directly ensure tx_buf_len cannot be zero to fix > the issue." > Ok, nice that you found it.
> Does the patch series look good to submit? > Yes, go ahead.
Jarkko
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