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Message-ID: <553934EB.4050701@broadcom.com>
Date: Thu, 23 Apr 2015 11:07:39 -0700
From: Jonathan Richardson <jonathar@...adcom.com>
To: Arnd Bergmann <arnd@...db.de>
CC: Scott Branden <sbranden@...adcom.com>,
Darren Edamura <dedamura@...adcom.com>,
Rob Herring <robh+dt@...nel.org>,
Pawel Moll <pawel.moll@....com>,
Mark Rutland <mark.rutland@....com>,
Ian Campbell <ijc+devicetree@...lion.org.uk>,
Kumar Gala <galak@...eaurora.org>, Ray Jui <rjui@...adcom.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
<devicetree@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<bcm-kernel-feedback-list@...adcom.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] misc: Add initial Digital Timing Engine (DTE) driver
for cygnus
Hi Arnd,
Thanks for the initial feedback. I'll investigate your suggestions and
get back to you if I have any questions before making some of the API
changes you've suggested.
On 15-04-23 01:04 AM, Arnd Bergmann wrote:
> On Wednesday 22 April 2015 16:22:03 Jonathan Richardson wrote:
>> Reviewed-by: Scott Branden <sbranden@...adcom.com>
>> Tested-by: Scott Branden <sbranden@...adcom.com>
>> Signed-off-by: Jonathan Richardson <jonathar@...adcom.com>
>
> No description at all?
>
> You are introducing a new subsystem here, which means you get to put
> a lot of thought into the API design, to ensure that it works with
> other drivers of the same type, and that we don't already have
> a subsystem that does what you need here.
>
> Please write a few pages of text about the tradeoffs that went into
> the internal and user-facing API design, and explain the differences
> to the existing infrastructure we have for the clocksource, clockevent,
> k_clock, posix timers, posix timers, timerfd, rtc, and ptp frameworks,
> in particular why your hardware cannot fit into the existing frameworks
> and has to have a new one.
>
>> +struct bcm_cygnus_dte *dte_get_dev_from_devname(const char *devname)
>> +{
>> + struct bcm_cygnus_dte *cygnus_dte = NULL;
>> + bool found = false;
>> +
>> + if (!devname)
>> + return NULL;
>> +
>> + list_for_each_entry(cygnus_dte, &dtedev_list, node) {
>> + if (!strcmp(dev_name(&cygnus_dte->pdev->dev), devname)) {
>> + /* Matched on device name */
>> + found = true;
>> + break;
>> + }
>> + }
>> +
>> + return found ? cygnus_dte : NULL;
>> +}
>> +EXPORT_SYMBOL(dte_get_dev_from_devname);
>
> No, don't match on a device name. If you must have a reference, use
> a phandle in DT.
>
>> +int dte_get_timestamp(
>> + struct bcm_cygnus_dte *cygnus_dte,
>> + enum dte_client client,
>> + struct timespec *ts)
>
> Please use timespec64 or ktime_t for internal interfaces.
>
>> + case DTE_IOCTL_SET_DIVIDER:
>
> For the IOCTLs, please write a documentation in man-page form. No need
> for troff formatting, plain text is fine.
>
>> +/**
>> + * DTE Client
>> + */
>> +enum dte_client {
>> + DTE_CLIENT_MIN = 0,
>> + DTE_CLIENT_I2S0_BITCLOCK = 0,
>> + DTE_CLIENT_I2S1_BITCLOCK,
>> + DTE_CLIENT_I2S2_BITCLOCK,
>> + DTE_CLIENT_I2S0_WORDCLOCK,
>> + DTE_CLIENT_I2S1_WORDCLOCK,
>> + DTE_CLIENT_I2S2_WORDCLOCK,
>> + DTE_CLIENT_LCD_CLFP,
>> + DTE_CLIENT_LCD_CLLP,
>> + DTE_CLIENT_GPIO14,
>> + DTE_CLIENT_GPIO15,
>> + DTE_CLIENT_GPIO22,
>> + DTE_CLIENT_GPIO23,
>> + DTE_CLIENT_MAX,
>> +};
>
> Make this more abstract, so we can reuse the API for other vendors.
>
>> +#define DTE_IOCTL_BASE 'd'
>> +#define DTE_IO(nr) _IO(DTE_IOCTL_BASE, nr)
>> +#define DTE_IOR(nr, type) _IOR(DTE_IOCTL_BASE, nr, type)
>> +#define DTE_IOW(nr, type) _IOW(DTE_IOCTL_BASE, nr, type)
>> +#define DTE_IOWR(nr, type) _IOWR(DTE_IOCTL_BASE, nr, type)
>> +
>> +#define DTE_IOCTL_SET_DIVIDER DTE_IOW(0x00, struct dte_data)
>> +#define DTE_IOCTL_ENABLE_TIMESTAMP DTE_IOW(0x01, struct dte_data)
>> +#define DTE_IOCTL_SET_IRQ_INTERVAL DTE_IOW(0x02, struct dte_data)
>> +#define DTE_IOCTL_GET_TIMESTAMP DTE_IOWR(0x03, struct dte_timestamp)
>> +#define DTE_IOCTL_SET_TIME DTE_IOW(0x04, struct timespec)
>> +#define DTE_IOCTL_GET_TIME DTE_IOR(0x05, struct timespec)
>
> Instead of timespec, use a pair of '__u64' values, or alternatively
> just a '__u64' for nanoseconds if the API does not have to cover
> times before 1970 or after 2262.
>
>> +#define DTE_IOCTL_ADJ_TIME DTE_IOW(0x06, int64_t)
>> +#define DTE_IOCTL_ADJ_FREQ DTE_IOW(0x07, int32_t)
>
> Maybe 'struct timex' for the adjustment?
>
> Also, how about adding new syscalls along the lines of
> the timerfd stuff instead of using ioctl?
>
>> +struct dte_data {
>> + enum dte_client client;
>> + unsigned int data;
>> +};
>
> No 'enum' in ioctl data, always use '__u32' etc.
>
>> +
>> +struct dte_timestamp {
>> + enum dte_client client;
>> + struct timespec ts;
>> +};
>
> Instead of timespec, use a pair of '__u64' values, or alternatively
> just a '__u64' for nanoseconds if the API does not have to cover
> times before 1970 or after 2262.
>
>> +struct bcm_cygnus_dte;
>> +
>> +extern struct bcm_cygnus_dte *dte_get_dev_from_devname(
>> + const char *devname);
>> +extern int dte_enable_timestamp(
>> + struct bcm_cygnus_dte *cygnus_dte,
>> + enum dte_client client,
>> + int enable);
>
>
> Put the internal declarations into one header in include/linux, and the
> user space facing ones in another one in include/uapi/linux.
>
> Arnd
>
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