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[2a01:c22:7af7:5300:8868:b389:215f:d1]) by smtp.googlemail.com with ESMTPSA id o3-20020a05600c4fc300b003cfbbd54178sm24538660wmq.2.2022.12.17.00.40.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 17 Dec 2022 00:40:42 -0800 (PST) Message-ID: Date: Fri, 16 Dec 2022 22:37:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 5/8] i2c: i801: add helper i801_set_hstadd() Content-Language: en-US To: Jean Delvare Cc: linux-i2c@vger.kernel.org References: <4125f9ce-ce5f-fbcf-7d6f-9bc586ac43e0@gmail.com> <20220609155326.30147f58@endymion.delvare> From: Heiner Kallweit In-Reply-To: <20220609155326.30147f58@endymion.delvare> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On 09.06.2022 15:53, Jean Delvare wrote: > Hi Heiner, > > On Fri, 15 Apr 2022 18:57:21 +0200, Heiner Kallweit wrote: >> Factor out setting SMBHSTADD to a helper. The current code makes the >> assumption that constant I2C_SMBUS_READ has bit 0 set, that's not ideal. > > This isn't an "assumption". The values of I2C_SMBUS_WRITE and > I2C_SMBUS_READ were chosen to match the bit position and values in the > I2C protocol. Maybe it should have been made clearer by defining them > as hexadecimal values instead of decimal values. Nevertheless, I find > it unfortunate to not use this fact to optimize the code, see below. > >> Therefore let the new helper explicitly check for I2C_SMBUS_READ. >> >> Signed-off-by: Heiner Kallweit >> --- >> drivers/i2c/busses/i2c-i801.c | 41 ++++++++++++++++++----------------- >> 1 file changed, 21 insertions(+), 20 deletions(-) >> >> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c >> index a9737f14d..bf77f8640 100644 >> --- a/drivers/i2c/busses/i2c-i801.c >> +++ b/drivers/i2c/busses/i2c-i801.c >> @@ -771,6 +771,14 @@ static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data * >> return result; >> } >> >> +static void i801_set_hstadd(struct i801_priv *priv, u8 addr, char read_write) >> +{ >> + addr <<= 1; >> + if (read_write == I2C_SMBUS_READ) >> + addr |= 0x01; >> + outb_p(addr, SMBHSTADD(priv)); > > This can be written: > > outb_p((addr << 1) | read_write, SMBHSTADD(priv)); > > Net result -48 bytes of (x86_64) binary code. That's basically what the > original code was doing, minus the useless masking. > OK >> +} >> + >> /* Return negative errno on error. */ >> static s32 i801_access(struct i2c_adapter *adap, u16 addr, >> unsigned short flags, char read_write, u8 command, >> @@ -795,28 +803,24 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr, >> >> switch (size) { >> case I2C_SMBUS_QUICK: >> - outb_p(((addr & 0x7f) << 1) | (read_write & 0x01), >> - SMBHSTADD(priv)); >> + i801_set_hstadd(priv, addr, read_write); >> xact = I801_QUICK; >> break; >> case I2C_SMBUS_BYTE: >> - outb_p(((addr & 0x7f) << 1) | (read_write & 0x01), >> - SMBHSTADD(priv)); >> + i801_set_hstadd(priv, addr, read_write); >> if (read_write == I2C_SMBUS_WRITE) >> outb_p(command, SMBHSTCMD(priv)); >> xact = I801_BYTE; >> break; >> case I2C_SMBUS_BYTE_DATA: >> - outb_p(((addr & 0x7f) << 1) | (read_write & 0x01), >> - SMBHSTADD(priv)); >> + i801_set_hstadd(priv, addr, read_write); >> outb_p(command, SMBHSTCMD(priv)); >> if (read_write == I2C_SMBUS_WRITE) >> outb_p(data->byte, SMBHSTDAT0(priv)); >> xact = I801_BYTE_DATA; >> break; >> case I2C_SMBUS_WORD_DATA: >> - outb_p(((addr & 0x7f) << 1) | (read_write & 0x01), >> - SMBHSTADD(priv)); >> + i801_set_hstadd(priv, addr, read_write); >> outb_p(command, SMBHSTCMD(priv)); >> if (read_write == I2C_SMBUS_WRITE) { >> outb_p(data->word & 0xff, SMBHSTDAT0(priv)); >> @@ -825,7 +829,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr, >> xact = I801_WORD_DATA; >> break; >> case I2C_SMBUS_PROC_CALL: >> - outb_p((addr & 0x7f) << 1, SMBHSTADD(priv)); >> + i801_set_hstadd(priv, addr, I2C_SMBUS_WRITE); >> outb_p(command, SMBHSTCMD(priv)); >> outb_p(data->word & 0xff, SMBHSTDAT0(priv)); >> outb_p((data->word & 0xff00) >> 8, SMBHSTDAT1(priv)); >> @@ -833,8 +837,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr, >> read_write = I2C_SMBUS_READ; >> break; >> case I2C_SMBUS_BLOCK_DATA: >> - outb_p(((addr & 0x7f) << 1) | (read_write & 0x01), >> - SMBHSTADD(priv)); >> + i801_set_hstadd(priv, addr, read_write); >> outb_p(command, SMBHSTCMD(priv)); >> block = 1; >> break; >> @@ -845,10 +848,11 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr, >> * However if SPD Write Disable is set (Lynx Point and later), >> * the read will fail if we don't set the R/#W bit. >> */ >> - outb_p(((addr & 0x7f) << 1) | >> - ((priv->original_hstcfg & SMBHSTCFG_SPD_WD) ? >> - (read_write & 0x01) : 0), >> - SMBHSTADD(priv)); >> + if (priv->original_hstcfg & SMBHSTCFG_SPD_WD) >> + i801_set_hstadd(priv, addr, read_write); >> + else >> + i801_set_hstadd(priv, addr, I2C_SMBUS_WRITE); > > Preserving the use of the ternary operator makes the generated binary > smaller once again: > > i801_set_hstadd(priv, addr, > (priv->original_hstcfg & SMBHSTCFG_SPD_WD) ? > read_write : I2C_SMBUS_WRITE); > > Net result -11 bytes of (x86_64) binary code. > OK >> + >> if (read_write == I2C_SMBUS_READ) { >> /* NB: page 240 of ICH5 datasheet also shows >> * that DATA1 is the cmd field when reading */ >> @@ -858,11 +862,8 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr, >> block = 1; >> break; >> case I2C_SMBUS_BLOCK_PROC_CALL: >> - /* >> - * Bit 0 of the slave address register always indicate a write >> - * command. >> - */ >> - outb_p((addr & 0x7f) << 1, SMBHSTADD(priv)); >> + /* Needs to be flagged as write transaction */ >> + i801_set_hstadd(priv, addr, I2C_SMBUS_WRITE); >> outb_p(command, SMBHSTCMD(priv)); >> block = 1; >> break; > >