From: Bitan Biswas <bbiswas@nvidia.com>
To: Dmitry Osipenko <digetx@gmail.com>,
Laxman Dewangan <ldewangan@nvidia.com>,
Thierry Reding <treding@nvidia.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
<linux-i2c@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, Peter Rosin <peda@axentia.se>,
Wolfram Sang <wsa@the-dreams.de>
Cc: Shardar Mohammed <smohammed@nvidia.com>,
Sowjanya Komatineni <skomatineni@nvidia.com>,
Mantravadi Karthik <mkarthik@nvidia.com>
Subject: Re: [PATCH V7] i2c: tegra: remove BUG, BUG_ON
Date: Mon, 17 Jun 2019 21:29:20 -0700 [thread overview]
Message-ID: <6ff6c8c8-7978-2662-266c-6122c5e2969b@nvidia.com> (raw)
In-Reply-To: <070ee927-be5a-327f-36d7-e6395c898574@gmail.com>
On 6/17/19 12:28 PM, Dmitry Osipenko wrote:
> 17.06.2019 21:41, Bitan Biswas пишет:
>>
>>
>> On 6/17/19 5:13 AM, Dmitry Osipenko wrote:
>>> 17.06.2019 8:09, Bitan Biswas пишет:
>>>> Remove BUG, BUG_ON as it makes system usable:
>>>> - Remove redundant BUG_ON calls or replace with WARN_ON_ONCE
>>>> as needed.
>>>> - Remove BUG() and mask Rx interrupt similar as Tx
>>>> for message fully sent case.
>>>> - Add caller error handling and WARN_ON_ONCE check for non-zero
>>>> rx_fifo_avail in tegra_i2c_empty_rx_fifo() after all processing.
>>>
>>> The commit message should describe motivation of the change and not the change itself,
>>> unless it's some additional information which is required for better understanding of
>>> the code.
>>>
>>> In yours case it could be something like that:
>>>
>>> The usage of BUG() macro is generally discouraged in kernel, unless
>>> it's a problem that results in a physical damage or loss of data.
>>> This patch removes unnecessary BUG() macros and replaces the rest
>>> with a warnings.
>> I shall update as per above comments.
>>
>>>
>>>> Signed-off-by: Bitan Biswas <bbiswas@nvidia.com>
>>>> ---
>>>> drivers/i2c/busses/i2c-tegra.c | 45 ++++++++++++++++++++++++++++++++++--------
>>>> 1 file changed, 37 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>>>> index 4dfb4c1..b155b61 100644
>>>> --- a/drivers/i2c/busses/i2c-tegra.c
>>>> +++ b/drivers/i2c/busses/i2c-tegra.c
>>>> @@ -73,6 +73,7 @@
>>>> #define I2C_ERR_NO_ACK BIT(0)
>>>> #define I2C_ERR_ARBITRATION_LOST BIT(1)
>>>> #define I2C_ERR_UNKNOWN_INTERRUPT BIT(2)
>>>> +#define I2C_ERR_RX_BUFFER_OVERFLOW BIT(3)
>>>> #define PACKET_HEADER0_HEADER_SIZE_SHIFT 28
>>>> #define PACKET_HEADER0_PACKET_ID_SHIFT 16
>>>> @@ -515,7 +516,11 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
>>>> * prevent overwriting past the end of buf
>>>> */
>>>> if (rx_fifo_avail > 0 && buf_remaining > 0) {
>>>> - BUG_ON(buf_remaining > 3);
>>>> + /*
>>>> + * buf_remaining > 3 check not needed as rx_fifo_avail == 0
>>>> + * when (words_to_transfer was > rx_fifo_avail) earlier
>>>> + * in this function.
>>>> + */
>>>> val = i2c_readl(i2c_dev, I2C_RX_FIFO);
>>>> val = cpu_to_le32(val);
>>>> memcpy(buf, &val, buf_remaining);
>>>> @@ -523,7 +528,15 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
>>>> rx_fifo_avail--;
>>>> }
>>>> - BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0);
>>>> + if ((!(i2c_dev->msg_buf_remaining)) &&
>>>
>>> The RX FIFO shall be drained completely no matter what.
>>>
>>> Hence why the "i2c_dev->msg_buf_remaining" checking is needed here?
>> I moved the part of below condition in Patch V6 to function tegra_i2c_empty_rx_fifo:
>>
>>>> + err_val = tegra_i2c_empty_rx_fifo(i2c_dev);
>>>> + if ((!(i2c_dev->msg_buf_remaining)) &&
>>
>>> Let's move this check into tegra_i2c_empty_rx_fifo() and return -EINVAL for that case.
>>> This will make code to look cleaner.
>>
>> Is above condition not needed?
>
> Let's put it at the very beginning. This may give a bit more information about the
> problem by knowing if the offending overflow happens after or during of the buffer's
> fill up.
>
> static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
> {
> u32 val;
> int rx_fifo_avail;
> u8 *buf = i2c_dev->msg_buf;
> size_t buf_remaining = i2c_dev->msg_buf_remaining;
> int words_to_transfer;
>
> if (WARN_ON(!i2c_dev->msg_buf_remaining))
> return -EINVAL;
> ...
>
OK
> In general, the original logic should be preserved during of refactoring. In this case
> we are keeping the original check and then also making it a bit more informative.
>
I feel the msg_buf_remaining check was not there in original code. The
corresponding line was probably the following checking for error when
(buf_remaining > 0) after all work in the function tegra_i2c_empty_rx_fifo()
https://elixir.bootlin.com/linux/v5.2-rc5/source/drivers/i2c/busses/i2c-tegra.c#L536
>>
>>>
>>> Secondly, in the future please don't add parens where they are not needed. In this
>>> case parens around !i2c_dev->msg_buf_remaining are not needed at all.
>>>
>> I shall look out for similar unnecessary parentheses and update the patch.
>
> Yes, please clean up all the occurrences in the code if there are any. And please do
> it in a separate patch.
>
I reviewed the source for unnecessary parentheses and do not find any.
Hence not planning to push any patch. Let me know if I missed a case.
-Thanks,
Bitan
prev parent reply other threads:[~2019-06-18 4:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-17 5:09 [PATCH V7] i2c: tegra: remove BUG, BUG_ON Bitan Biswas
2019-06-17 12:13 ` Dmitry Osipenko
2019-06-17 18:41 ` Bitan Biswas
2019-06-17 19:28 ` Dmitry Osipenko
2019-06-18 4:29 ` Bitan Biswas [this message]
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