From: Michael Hennerich <michael.hennerich@analog.com> To: Lars-Peter Clausen <lars@metafoo.de>, <jic23@kernel.org>, <knaack.h@gmx.de>, <pmeerw@pmeerw.net>, <robh+dt@kernel.org>, <mark.rutland@arm.com> Cc: <linux-iio@vger.kernel.org>, <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org> Subject: Re: [PATCH] iio/adc/ltc2497: Driver for Linear Technology LTC2497 ADC Date: Wed, 29 Mar 2017 10:51:57 +0200 [thread overview] Message-ID: <025f8461-c823-1f07-5742-e488c3e34f9f@analog.com> (raw) In-Reply-To: <6774c073-7fe4-e259-306e-3cf4621f7c69@metafoo.de> On 23.03.2017 12:05, Lars-Peter Clausen wrote: Sorry - I missed some of this review feedback ... >> + >> +static int ltc2497_wait_conv(struct ltc2497_st *st) >> +{ >> + s64 time_elapsed; >> + >> + time_elapsed = ktime_ms_delta(ktime_get(), st->time_prev); >> + >> + if (time_elapsed < LTC2497_CONVERSION_TIME_MS) { >> + /* delay if conversion time not passed >> + * since last read or write >> + */ >> + msleep(LTC2497_CONVERSION_TIME_MS - time_elapsed); > > Considering how long this sleeps msleep_interruptible() might be the better > choice. Wondering what should be the outcome of this? We can't simply replace it. Actually I've seen cases here in drivers/iio where the delay is essential, but the return value of msleep_interruptible() is not being checked. Thus causing a malicious access, in case a signal is received. We must delay here. If we switch to msleep_interruptible() the only reason for this would be to cancel the read and return -EINTR to the user. Also there is another msleep below which would also need this kind of handling. > >> + return 0; >> + } >> + >> + if (time_elapsed - LTC2497_CONVERSION_TIME_MS <= 0) { >> + /* We're in automatic mode - >> + * so the last reading is stil not outdated >> + */ >> + return 0; >> + } >> + >> + return -ETIMEDOUT; >> +} >> + >> +static int ltc2497_read(struct ltc2497_st *st, u8 address, int *val) >> +{ >> + struct i2c_client *client = st->client; >> + __be32 buf = 0; > > transfer buffers must not be on the stack to avoid issues if the controller > should use DMA. > >> + int ret; >> + >> + ret = ltc2497_wait_conv(st); >> + if (ret < 0 || st->addr_prev != address) { >> + ret = i2c_smbus_write_byte(st->client, 0xA0 | address); >> + if (ret < 0) >> + return ret; >> + st->addr_prev = address; >> + msleep(LTC2497_CONVERSION_TIME_MS); >> + } >> + ret = i2c_master_recv(client, (char *)&buf, 3); >> + if (ret < 0) { >> + dev_err(&client->dev, "i2c_master_recv failed\n"); >> + return ret; >> + } >> + st->time_prev = ktime_get(); >> + *val = (be32_to_cpu(buf) >> 14) - (1 << 17); >> + >> + return ret; >> +} > [...] > -- Greetings, Michael -- Analog Devices GmbH Otl-Aicher Strasse 60-64 80807 München Sitz der Gesellschaft München, Registergericht München HRB 40368, Geschäftsführer: Peter Kolberg, Ali Raza Husain, Eileen Wynne
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From: Michael Hennerich <michael.hennerich-OyLXuOCK7orQT0dZR+AlfA@public.gmane.org> To: Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>, jic23-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, knaack.h-Mmb7MZpHnFY@public.gmane.org, pmeerw-jW+XmwGofnusTnJN9+BGXg@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org Cc: linux-iio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Subject: Re: [PATCH] iio/adc/ltc2497: Driver for Linear Technology LTC2497 ADC Date: Wed, 29 Mar 2017 10:51:57 +0200 [thread overview] Message-ID: <025f8461-c823-1f07-5742-e488c3e34f9f@analog.com> (raw) In-Reply-To: <6774c073-7fe4-e259-306e-3cf4621f7c69-Qo5EllUWu/uELgA04lAiVw@public.gmane.org> On 23.03.2017 12:05, Lars-Peter Clausen wrote: Sorry - I missed some of this review feedback ... >> + >> +static int ltc2497_wait_conv(struct ltc2497_st *st) >> +{ >> + s64 time_elapsed; >> + >> + time_elapsed = ktime_ms_delta(ktime_get(), st->time_prev); >> + >> + if (time_elapsed < LTC2497_CONVERSION_TIME_MS) { >> + /* delay if conversion time not passed >> + * since last read or write >> + */ >> + msleep(LTC2497_CONVERSION_TIME_MS - time_elapsed); > > Considering how long this sleeps msleep_interruptible() might be the better > choice. Wondering what should be the outcome of this? We can't simply replace it. Actually I've seen cases here in drivers/iio where the delay is essential, but the return value of msleep_interruptible() is not being checked. Thus causing a malicious access, in case a signal is received. We must delay here. If we switch to msleep_interruptible() the only reason for this would be to cancel the read and return -EINTR to the user. Also there is another msleep below which would also need this kind of handling. > >> + return 0; >> + } >> + >> + if (time_elapsed - LTC2497_CONVERSION_TIME_MS <= 0) { >> + /* We're in automatic mode - >> + * so the last reading is stil not outdated >> + */ >> + return 0; >> + } >> + >> + return -ETIMEDOUT; >> +} >> + >> +static int ltc2497_read(struct ltc2497_st *st, u8 address, int *val) >> +{ >> + struct i2c_client *client = st->client; >> + __be32 buf = 0; > > transfer buffers must not be on the stack to avoid issues if the controller > should use DMA. > >> + int ret; >> + >> + ret = ltc2497_wait_conv(st); >> + if (ret < 0 || st->addr_prev != address) { >> + ret = i2c_smbus_write_byte(st->client, 0xA0 | address); >> + if (ret < 0) >> + return ret; >> + st->addr_prev = address; >> + msleep(LTC2497_CONVERSION_TIME_MS); >> + } >> + ret = i2c_master_recv(client, (char *)&buf, 3); >> + if (ret < 0) { >> + dev_err(&client->dev, "i2c_master_recv failed\n"); >> + return ret; >> + } >> + st->time_prev = ktime_get(); >> + *val = (be32_to_cpu(buf) >> 14) - (1 << 17); >> + >> + return ret; >> +} > [...] > -- Greetings, Michael -- Analog Devices GmbH Otl-Aicher Strasse 60-64 80807 München Sitz der Gesellschaft München, Registergericht München HRB 40368, Geschäftsführer: Peter Kolberg, Ali Raza Husain, Eileen Wynne
next prev parent reply other threads:[~2017-03-29 8:51 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-23 10:35 [PATCH] iio/adc/ltc2497: Driver for Linear Technology LTC2497 ADC michael.hennerich 2017-03-23 10:35 ` michael.hennerich 2017-03-23 11:05 ` Lars-Peter Clausen 2017-03-23 11:05 ` Lars-Peter Clausen 2017-03-29 8:51 ` Michael Hennerich [this message] 2017-03-29 8:51 ` Michael Hennerich 2017-03-23 11:28 ` Peter Meerwald-Stadler 2017-03-23 11:28 ` Peter Meerwald-Stadler 2017-03-23 14:45 ` Michael Hennerich 2017-03-23 14:45 ` Michael Hennerich
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