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Message-ID: <20121007194717.GE12801@game.jcrosoft.org>
Date: Sun, 7 Oct 2012 21:47:17 +0200
From: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
To: Roland Stigge <stigge@...com.de>
Cc: grant.likely@...retlab.ca, linus.walleij@...aro.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
w.sang@...gutronix.de, jbe@...gutronix.de, highguy@...il.com,
broonie@...nsource.wolfsonmicro.com
Subject: Re: [PATCH RFC 1/2 v2] gpio: Add a block GPIO API to gpiolib
On 22:36 Fri 05 Oct , Roland Stigge wrote:
> The recurring task of providing simultaneous access to GPIO lines (especially
> for bit banging protocols) needs an appropriate API.
>
> This patch adds a kernel internal "Block GPIO" API that enables simultaneous
> access to several GPIOs. This is done by abstracting GPIOs to an n-bit word:
> Once requested, it provides access to a group of GPIOs which can range over
> multiple GPIO chips.
>
> Signed-off-by: Roland Stigge <stigge@...com.de>
>
> ---
> NOTE: This is only useful if individual drivers implement the .get_block() and
> .set_block() functions. I'm providing an example implementation for max730x
> (see next patch), and can provide further driver patches after API review.
>
> Thanks in advance!
>
> Documentation/gpio.txt | 39 +++++++++++
> drivers/gpio/gpiolib.c | 148 +++++++++++++++++++++++++++++++++++++++++++++
> include/asm-generic/gpio.h | 10 +++
> include/linux/gpio.h | 67 ++++++++++++++++++++
> 4 files changed, 264 insertions(+)
>
> --- linux-2.6.orig/Documentation/gpio.txt
> +++ linux-2.6/Documentation/gpio.txt
> @@ -439,6 +439,45 @@ slower clock delays the rising edge of S
> signaling rate accordingly.
>
>
> +Block GPIO
> +----------
> +
> +The above described interface concentrates on handling single GPIOs. However,
> +in applications where it is critical to set several GPIOs at once, this
> +interface doesn't work well, e.g. bit-banging protocols via GPIO lines.
> +Consider a GPIO controller that is connected via a slow I2C line. When
> +switching two or more GPIOs one after another, there can be considerable time
> +between those events. This is solved by an interface called Block GPIO:
> +
> +struct gpio_block *gpio_block_request(unsigned int *gpios, size_t size);
> +
> +This creates a new block of GPIOs as a list of GPIO numbers with the specified
> +size which are accessible via the returned struct gpio_block and the accessor
> +functions described below. Please note that you need to request the GPIOs
> +separately via gpio_request(). An arbitrary list of globally valid GPIOs can be
> +specified, even ranging over several gpio_chips. Actual handling of I/O
> +operations will be done on a best effort base, i.e. simultaneous I/O only where
> +possible by hardware and implemented in the respective GPIO driver. The number
> +of GPIOs in one block is limited to 32 on a 32 bit system, and 64 on a 64 bit
> +system.
this limitation is not acceptable use an helper to generate an array as done
for the request so you can do a prepare bofore do set or get which both will
take on arrays as params and return int as status
Best Regards,
J.
> +
> +
> What do these conventions omit?
> ===============================
> One of the biggest things these conventions omit is pin multiplexing, since
> --- linux-2.6.orig/drivers/gpio/gpiolib.c
> +++ linux-2.6/drivers/gpio/gpiolib.c
> @@ -1676,6 +1676,154 @@ void __gpio_set_value(unsigned gpio, int
> }
> EXPORT_SYMBOL_GPL(__gpio_set_value);
>
> +static inline
> +int gpio_block_chip_index(struct gpio_block *block, struct gpio_chip *gc)
> +{
> + int i;
> +
> + for (i = 0; i < block->nchip; i++) {
> + if (block->gbc[i].gc == gc)
> + return i;
> + }
> + return -1;
> +}
> +
> +struct gpio_block *__gpio_block_request(unsigned *gpios, size_t size)
> +{
> + struct gpio_block *block;
> + struct gpio_block_chip *gbc;
> + struct gpio_remap *remap;
> + int i;
> +
> + if (size < 1 || size > sizeof(unsigned) * 8)
> + return NULL;
> +
> + block = kzalloc(sizeof(struct gpio_block), GFP_KERNEL);
> +
> + for (i = 0; i < size; i++) {
> + struct gpio_chip *gc = gpio_to_chip(gpios[i]);
> + int bit = gpios[i] - gc->base;
> + int index = gpio_block_chip_index(block, gc);
> +
> + if (index < 0) {
> + block->nchip++;
> + block->gbc = krealloc(block->gbc,
> + sizeof(struct gpio_block_chip) *
> + block->nchip, GFP_KERNEL);
> + gbc = &block->gbc[block->nchip - 1];
> + gbc->gc = gc;
> + gbc->remap = NULL;
> + gbc->nremap = 0;
> + gbc->mask = 0;
> + } else {
> + gbc = &block->gbc[index];
> + }
> + /* represents the mask necessary on calls to the driver's
> + * .get_block() and .set_block()
> + */
> + gbc->mask |= BIT(bit);
> +
> + /* collect gpios that are specified together, represented by
> + * neighboring bits
> + */
> + remap = &gbc->remap[gbc->nremap - 1];
> + if (!gbc->nremap || !(remap->mask & BIT(i - 1))) {
> + gbc->nremap++;
> + gbc->remap = krealloc(gbc->remap,
> + sizeof(struct gpio_remap) *
> + gbc->nremap, GFP_KERNEL);
> + remap = &gbc->remap[gbc->nremap - 1];
> + remap->offset = bit - i;
> + remap->mask = 0;
> + }
> +
> + /* represents the mask necessary for bit reordering between
> + * gpio_block (i.e. as specified on gpio_block_get() and
> + * gpio_block_set()) and gpio_chip domain (i.e. as specified on
> + * the driver's .set_block() and .get_block())
> + */
> + remap->mask |= BIT(i);
> + }
> +
> + return block;
> +}
> +EXPORT_SYMBOL_GPL(__gpio_block_request);
> +
> +void __gpio_block_free(struct gpio_block *block)
> +{
> + int i;
> +
> + for (i = 0; i < block->nchip; i++)
> + kfree(block->gbc[i].remap);
> + kfree(block->gbc);
> + kfree(block);
> +}
> +EXPORT_SYMBOL_GPL(__gpio_block_free);
> +
> +unsigned __gpio_block_get(struct gpio_block *block)
> +{
> + struct gpio_block_chip *gbc;
> + int i, j;
> + unsigned values = 0;
> +
> + for (i = 0; i < block->nchip; i++) {
> + unsigned remapped = 0;
> +
> + gbc = &block->gbc[i];
> +
> + if (gbc->gc->get_block) {
> + remapped = gbc->gc->get_block(gbc->gc, gbc->mask);
> + } else { /* emulate */
> + unsigned bit = 1;
> +
> + for (j = 0; j < sizeof(unsigned) * 8; j++, bit <<= 1) {
> + if (gbc->mask & bit)
> + remapped |= gbc->gc->get(gbc->gc,
> + gbc->gc->base + j) << j;
> + }
> + }
> +
> + for (j = 0; j < gbc->nremap; j++) {
> + struct gpio_remap *gr = &gbc->remap[j];
> +
> + values |= (remapped >> gr->offset) & gr->mask;
> + }
> + }
> +
> + return values;
> +}
> +EXPORT_SYMBOL_GPL(__gpio_block_get);
> +
> +void __gpio_block_set(struct gpio_block *block, unsigned values)
> +{
> + struct gpio_block_chip *gbc;
> + int i, j;
> +
> + for (i = 0; i < block->nchip; i++) {
> + unsigned remapped = 0;
> +
> + gbc = &block->gbc[i];
> +
> + for (j = 0; j < gbc->nremap; j++) {
> + struct gpio_remap *gr = &gbc->remap[j];
> +
> + remapped |= (values & gr->mask) << gr->offset;
> + }
> + if (gbc->gc->set_block) {
> + gbc->gc->set_block(gbc->gc, gbc->mask, remapped);
> + } else { /* emulate */
> + unsigned bit = 1;
> +
> + for (j = 0; j < sizeof(unsigned) * 8; j++, bit <<= 1) {
> + if (gbc->mask & bit)
> + gbc->gc->set(gbc->gc, gbc->gc->base + j,
> + (remapped >> j) & 1);
> + }
> + }
> + }
> +}
> +EXPORT_SYMBOL_GPL(__gpio_block_set);
> +
> /**
> * __gpio_cansleep() - report whether gpio value access will sleep
> * @gpio: gpio in question
> --- linux-2.6.orig/include/asm-generic/gpio.h
> +++ linux-2.6/include/asm-generic/gpio.h
> @@ -43,6 +43,7 @@ static inline bool gpio_is_valid(int num
>
> struct device;
> struct gpio;
> +struct gpio_block;
> struct seq_file;
> struct module;
> struct device_node;
> @@ -105,6 +106,8 @@ struct gpio_chip {
> unsigned offset);
> int (*get)(struct gpio_chip *chip,
> unsigned offset);
> + unsigned (*get_block)(struct gpio_chip *chip,
> + unsigned mask);
> int (*direction_output)(struct gpio_chip *chip,
> unsigned offset, int value);
> int (*set_debounce)(struct gpio_chip *chip,
> @@ -112,6 +115,8 @@ struct gpio_chip {
>
> void (*set)(struct gpio_chip *chip,
> unsigned offset, int value);
> + void (*set_block)(struct gpio_chip *chip,
> + unsigned mask, unsigned values);
>
> int (*to_irq)(struct gpio_chip *chip,
> unsigned offset);
> @@ -171,6 +176,11 @@ extern void gpio_set_value_cansleep(unsi
> extern int __gpio_get_value(unsigned gpio);
> extern void __gpio_set_value(unsigned gpio, int value);
>
> +extern struct gpio_block *__gpio_block_request(unsigned *gpio, size_t size);
> +extern void __gpio_block_free(struct gpio_block *block);
> +extern unsigned __gpio_block_get(struct gpio_block *block);
> +extern void __gpio_block_set(struct gpio_block *block, unsigned values);
> +
> extern int __gpio_cansleep(unsigned gpio);
>
> extern int __gpio_to_irq(unsigned gpio);
> --- linux-2.6.orig/include/linux/gpio.h
> +++ linux-2.6/include/linux/gpio.h
> @@ -2,6 +2,7 @@
> #define __LINUX_GPIO_H
>
> #include <linux/errno.h>
> +#include <linux/types.h>
>
> /* see Documentation/gpio.txt */
>
> @@ -39,6 +40,27 @@ struct gpio {
> const char *label;
> };
>
> +struct gpio_remap {
> + int mask;
> + int offset;
> +};
> +
> +struct gpio_block_chip {
> + struct gpio_chip *gc;
> + struct gpio_remap *remap;
> + int nremap;
> + unsigned mask;
> +};
> +
> +/**
> + * struct gpio_block - a structure describing a list of GPIOs for simultaneous
> + * operations
> + */
> +struct gpio_block {
> + struct gpio_block_chip *gbc;
> + size_t nchip;
> +};
> +
> #ifdef CONFIG_GENERIC_GPIO
>
> #ifdef CONFIG_ARCH_HAVE_CUSTOM_GPIO_H
> @@ -57,6 +79,28 @@ static inline void gpio_set_value(unsign
> __gpio_set_value(gpio, value);
> }
>
> +static inline
> +struct gpio_block *gpio_block_request(unsigned int *gpios, size_t size)
> +{
> + return __gpio_block_request(gpios, size);
> +}
> +
> +static inline void gpio_block_free(struct gpio_block *block)
> +{
> + __gpio_block_free(block);
> +}
> +
> +static inline unsigned gpio_block_get(struct gpio_block *block)
> +{
> + return __gpio_block_get(block, value);
> +}
> +
> +static inline
> +void gpio_block_set(struct gpio_block *block, unsigned value)
> +{
> + __gpio_block_set(block, value);
> +}
> +
> static inline int gpio_cansleep(unsigned int gpio)
> {
> return __gpio_cansleep(gpio);
> @@ -169,6 +213,29 @@ static inline void gpio_set_value(unsign
> WARN_ON(1);
> }
>
> +static inline
> +struct gpio_block *gpio_block_request(unsigned int *gpios, size_t size)
> +{
> + WARN_ON(1);
> + return NULL;
> +}
> +
> +static inline void gpio_block_free(struct gpio_block *block)
> +{
> + WARN_ON(1);
> +}
> +
> +static inline unsigned gpio_block_get(struct gpio_block *block)
> +{
> + WARN_ON(1);
> + return 0;
> +}
> +
> +static inline void gpio_block_set(struct gpio_block *block, unsigned value)
> +{
> + WARN_ON(1);
> +}
> +
> static inline int gpio_cansleep(unsigned gpio)
> {
> /* GPIO can never have been requested or set as {in,out}put */
--
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