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[2a01:c23:c4bc:ff00:1041:a2b8:3c58:ba6d]) by smtp.googlemail.com with ESMTPSA id v14-20020adff68e000000b002365730eae8sm27354723wrp.55.2023.01.16.13.59.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jan 2023 13:59:29 -0800 (PST) Message-ID: <22af23f5-f037-2b3b-a31b-a978e6957ed3@gmail.com> Date: Mon, 16 Jan 2023 22:22:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH v3 2/3] i2c: algo: bit: allow getsda to be NULL Content-Language: en-US To: Peter Rosin , Rob Herring , Krzysztof Kozlowski , Wolfram Sang Cc: "linux-i2c@vger.kernel.org" , "devicetree@vger.kernel.org" References: <3a5545f3-f858-2c80-8bd4-2e0d401a1dc0@gmail.com> <7ebc1687-d962-d087-aaba-33f62fa65f8a@axentia.se> From: Heiner Kallweit In-Reply-To: <7ebc1687-d962-d087-aaba-33f62fa65f8a@axentia.se> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 16.01.2023 08:17, Peter Rosin wrote: > Hi! > > 2023-01-15 at 11:15, Heiner Kallweit wrote: >> This is in preparation of supporting write-only SDA in i2c-gpio. >> >> Signed-off-by: Heiner Kallweit >> --- >> v3: >> - check for adap->getsda in readbytes() >> - align warning message level for info on missing getscl/getsda >> --- >> drivers/i2c/algos/i2c-algo-bit.c | 16 ++++++++++++++-- >> 1 file changed, 14 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/i2c/algos/i2c-algo-bit.c b/drivers/i2c/algos/i2c-algo-bit.c >> index fc90293af..a1b822723 100644 >> --- a/drivers/i2c/algos/i2c-algo-bit.c >> +++ b/drivers/i2c/algos/i2c-algo-bit.c >> @@ -184,8 +184,9 @@ static int i2c_outb(struct i2c_adapter *i2c_adap, unsigned char c) >> >> /* read ack: SDA should be pulled down by slave, or it may >> * NAK (usually to report problems with the data we wrote). >> + * Always report ACK if SDA is write-only. >> */ >> - ack = !getsda(adap); /* ack: sda is pulled low -> success */ >> + ack = !adap->getsda || !getsda(adap); /* ack: sda is pulled low -> success */ >> bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c, >> ack ? "A" : "NA"); >> >> @@ -232,6 +233,10 @@ static int test_bus(struct i2c_adapter *i2c_adap) >> const char *name = i2c_adap->name; >> int scl, sda, ret; >> >> + /* Testing not possible if both pins are write-only. */ >> + if (adap->getscl == NULL && adap->getsda == NULL) >> + return 0; > > Would it not be nice to keep output-only SCL and SDA independent? With > your proposed check before doing the tests, all tests will crash when > adap->getsda is NULL, unless adap->getscl also happens to be NULL. > > So, I would like to remove the above check and instead see some changes > along the lines of > > - sda = getsda(adap); > + sda = (adap->getsda == NULL) ? 1 : getsda(adap); > > (BTW, I dislike this way of writing that, and would have written > sda = adap->getsda ? getsda(adap) : 1; > had it not been for the preexisting code for the SCL case. Oh well.) > Right, I'll change it accordingly in v2. >> + >> if (adap->pre_xfer) { >> ret = adap->pre_xfer(i2c_adap); >> if (ret < 0) >> @@ -420,6 +425,10 @@ static int readbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg) >> unsigned char *temp = msg->buf; >> int count = msg->len; >> const unsigned flags = msg->flags; >> + struct i2c_algo_bit_data *adap = i2c_adap->algo_data; >> + >> + if (!adap->getsda) >> + return -EOPNOTSUPP; >> >> while (count > 0) { >> inval = i2c_inb(i2c_adap); >> @@ -670,8 +679,11 @@ static int __i2c_bit_add_bus(struct i2c_adapter *adap, >> if (ret < 0) >> return ret; >> >> - /* Complain if SCL can't be read */ >> + if (bit_adap->getsda == NULL) >> + dev_warn(&adap->dev, "Not I2C compliant: can't read SDA\n"); >> + >> if (bit_adap->getscl == NULL) { >> + /* Complain if SCL can't be read */ >> dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n"); >> dev_warn(&adap->dev, "Bus may be unreliable\n"); >> } > > And here you'd need something like this to make them independently select-able: > > if (bit_adap->getsda == NULL) > dev_warn(&adap->dev, "Not I2C compliant: can't read SDA\n"); > > if (bit_adap->getscl == NULL) > dev_warn(&adap->dev, "Not I2C compliant: can't read SCL\n"); > > if (bit_adap->getscl == NULL || bit_adap->getsda == NULL) > dev_warn(&adap->dev, "Bus may be unreliable\n"); > Will be changed accordingly in v2. > Anyway, as is, this patch is broken if getsda is NULL while getscl is not. > There is no documentation describing that limitation. It looks easier to > fix the limitation than to muddy the waters by having ifs and buts. > > Cheers, > Peter