From: Jarkko Nikula <jarkko.nikula@linux.intel.com>
To: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: aaron.ma@canonical.com, admin@kryma.net,
andriy.shevchenko@linux.intel.com, benjamin.tissoires@redhat.com,
hdegoede@redhat.com, hn.chen@weidahitech.com, jikos@kernel.org,
kai.heng.feng@canonical.com, linux-i2c@vger.kernel.org,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
mika.westerberg@linux.intel.com, vicamo.yang@canonical.com,
wsa@kernel.org
Subject: Re: [PATCH v3] i2c: Squash of SMBus block read patchset to save power
Date: Wed, 16 Sep 2020 17:09:18 +0300 [thread overview]
Message-ID: <796a23d2-cb98-c431-3494-b59044189468@linux.intel.com> (raw)
In-Reply-To: <20200915174844.GA16807@sultan-box.localdomain>
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
next prev parent reply other threads:[~2020-09-16 17:51 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-14 21:02 [PATCH 0/2] i2c-hid: Save power by reducing i2c xfers with block reads Sultan Alsawaf
2020-06-14 21:02 ` [PATCH 1/2] i2c: designware: Only check the first byte for SMBus block read length Sultan Alsawaf
2020-06-15 9:40 ` Andy Shevchenko
2020-06-15 16:03 ` Sultan Alsawaf
2020-06-15 16:07 ` Andy Shevchenko
2020-06-15 17:15 ` Sultan Alsawaf
2020-06-16 13:22 ` Jarkko Nikula
2020-06-16 15:43 ` [PATCH v2] " Sultan Alsawaf
2020-06-17 11:08 ` Jarkko Nikula
2020-06-14 21:02 ` [PATCH 2/2] HID: i2c-hid: Use block reads when possible to save power Sultan Alsawaf
2020-06-16 13:43 ` Jarkko Nikula
2020-06-16 15:49 ` [PATCH v2] " Sultan Alsawaf
2020-06-16 16:41 ` Andy Shevchenko
2020-06-16 17:18 ` Andi Shyti
2020-06-16 17:32 ` Sultan Alsawaf
2020-06-16 18:02 ` Andi Shyti
2020-06-16 18:17 ` Sultan Alsawaf
2020-06-17 11:17 ` Jarkko Nikula
2020-06-29 17:43 ` Sultan Alsawaf
2020-07-01 8:04 ` Jarkko Nikula
2020-07-01 15:00 ` Sultan Alsawaf
2020-07-03 11:18 ` Jarkko Nikula
2020-09-14 0:15 ` [PATCH v3] i2c: Squash of SMBus block read patchset " Sultan Alsawaf
[not found] ` <bcf9cd02-13d1-8f87-8ef9-2f05f0b54808@linux.intel.com>
2020-09-15 17:48 ` Sultan Alsawaf
2020-09-16 14:09 ` Jarkko Nikula [this message]
2020-09-15 20:44 ` Jiri Kosina
2020-06-22 0:58 ` [HID] 0b987151f0: kmsg.i2c_designware_i2c_designware.#: controller_timed_out kernel test robot
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