From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bitan Biswas Subject: Re: [PATCH V7] i2c: tegra: remove BUG, BUG_ON Date: Mon, 17 Jun 2019 11:41:00 -0700 Message-ID: <43a3fae8-dd3e-c7d3-42a7-493210e601e2@nvidia.com> References: <1560748152-6575-1-git-send-email-bbiswas@nvidia.com> <5a8ad23f-33c8-5140-cef8-f9cef70764b1@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <5a8ad23f-33c8-5140-cef8-f9cef70764b1@gmail.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko , Laxman Dewangan , Thierry Reding , Jonathan Hunter , linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Rosin , Wolfram Sang Cc: Shardar Mohammed , Sowjanya Komatineni , Mantravadi Karthik List-Id: linux-tegra@vger.kernel.org On 6/17/19 5:13 AM, Dmitry Osipenko wrote: > 17.06.2019 8:09, Bitan Biswas =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> 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. >=20 > The commit message should describe motivation of the change and not the c= hange itself, > unless it's some additional information which is required for better unde= rstanding of > the code. >=20 > In yours case it could be something like that: >=20 > 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. >=20 >> Signed-off-by: Bitan Biswas >> --- >> 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-teg= ra.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) >> =20 >> #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 =3D=3D 0 >> + * when (words_to_transfer was > rx_fifo_avail) earlier >> + * in this function. >> + */ >> val =3D i2c_readl(i2c_dev, I2C_RX_FIFO); >> val =3D 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--; >> } >> =20 >> - BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0); >> + if ((!(i2c_dev->msg_buf_remaining)) && >=20 > The RX FIFO shall be drained completely no matter what. >=20 > Hence why the "i2c_dev->msg_buf_remaining" checking is needed here? I moved the part of below condition in Patch V6 to function=20 tegra_i2c_empty_rx_fifo: >> + err_val =3D 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=20 -EINVAL for that case. > This will make code to look cleaner. Is above condition not needed? >=20 > 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. >=20 I shall look out for similar unnecessary parentheses and update the patch. >> + WARN_ON_ONCE(rx_fifo_avail)) >> + return -EINVAL; >> + >> + /* >> + * buf_remaining > 0 at this point can only have rx_fifo_avail =3D=3D = 0 >=20 > The rx_fifo_avail is always 0 at this point, including the case of buf_re= maining =3D=3D 0. > It will be better if you'll add a comment for the WARN_ON_ONCE(rx_fifo_av= ail) above, > saying that RX FIFO must be fully drained, and then just drop this commen= t. >=20 OK. >> + * as this corresponds to (words_to_transfer was > rx_fifo_avail) >> + * case earlier in this function. >> + */ >> i2c_dev->msg_buf_remaining =3D buf_remaining; >> i2c_dev->msg_buf =3D buf; >=20 > [snip] >=20