Re: [PATCH 2/2] spi: spi-pic32: Add PIC32 SPI master driver

[Purna Chandra Mandal]

Hi Mark,

On 02/02/2016 05:43 PM, Mark Brown wrote:

> On Mon, Feb 01, 2016 at 03:44:57PM -0700, Joshua Henderson wrote:
>
>> The PIC32 SPI driver is capable of performing SPI transfers either using
>> polling or based on interrupt-trigger. GPIO based CS support (necessary
>> for correct SPI operation) is available. It is dependent on availability
>> of "cs-gpios" property of spi node in board dts file.
> There's quite a lot of issues here.  At a high level the big issues are
> with duplicating core functionality, a large number of helper functions
> that don't seem to add much and some interesting locking.  There's also
> no DT binding documentation which is mandatory for new bindings.

Good summary, will remove the helper functions wherever required. Also fix
locking issue, and implement transfer_one().

Please find the binding documentation (missed adding you in CC).
https://patchwork.ozlabs.org/patch/576738/

>> +config SPI_PIC32
>> +	tristate "Microchip PIC32 series SPI"
>> +	depends on MACH_PIC32
>> +	help
>> +	  SPI driver for PIC32 SPI master controller.
>> +
>> +
>>  #
>>  # Add new SPI master controllers in alphabetical order above this line
>>  #
> Note the comment here (yes, there are some things out of order but
> that's no reason to add more).  Please also add an || COMPILE_TEST
> unless there's an actual build time dependency.

Ack, Will add in alphabetical order and add || COMPILE_TEST.

>> diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
>> index 8991ffc..bb37fed 100644
>> --- a/drivers/spi/Makefile
>> +++ b/drivers/spi/Makefile
>> @@ -94,3 +94,4 @@ obj-$(CONFIG_SPI_XILINX)		+= spi-xilinx.o
>>  obj-$(CONFIG_SPI_XLP)			+= spi-xlp.o
>>  obj-$(CONFIG_SPI_XTENSA_XTFPGA)		+= spi-xtensa-xtfpga.o
>>  obj-$(CONFIG_SPI_ZYNQMP_GQSPI)		+= spi-zynqmp-gqspi.o
>> +obj-$(CONFIG_SPI_PIC32)			+= spi-pic32.o
> Similarly here where things are better sorted already.

ack, Will add in sorted order.

>> +/*
>> + * PIC32 SPI core controller driver (refer dw_spi.c)
> What should we refer to dw_spi.c for?  If this is a Designware IP you
> should share the same driver.

This is Microchip proprietary SPI IP, not Designware. Reference to dw_spi.c here
is to mention 'inspired by'. Will update comment accordingly.

>> +static inline void spi_disable_chip(struct pic32_spi *pic32s)
>> +{
>> +	writel(SPICON_ON, pic32s->regs + SPICON_CLR);
>> +	cpu_relax();
>> +}
> What is the cpu_relax() intended to do here?

No SPI registers may be read or written in the CPU cycle immediately following
the instruction that clears the module’s ON bit.
Is there any better alternative than this? or udelay()? anyway, will add comment why this is here.

>> +static inline void spi_set_clk_mode(struct pic32_spi *pic32s, int mode)
>> +{
>> +	u32 conset = 0, conclr = 0;
>> +
>> +	/* active low */
>> +	if (mode & SPI_CPOL)
>> +		conset |= SPICON_CKP;
>> +	else
>> +		conclr |= SPICON_CKP;
>> +
>> +	/* tx on rising edge of clk */
>> +	if (mode & SPI_CPHA)
>> +		conclr |= SPICON_CKE;
>> +	else
>> +		conset |= SPICON_CKE;
>> +
>> +	/* rx at end of tx */
>> +	conset |= SPICON_SMP;
>> +
>> +	writel(conclr, pic32s->regs + SPICON_CLR);
>> +	writel(conset, pic32s->regs + SPICON_SET);
>> +}
> This is large for an inline function and only has one caller anyway.
> Why not just include it in that user?

ack. Merge accordingly,

>> +static inline void spi_drain_rx_buf(struct pic32_spi *pic32s)
>> +{
>> +	u32 sr;
>> +
>> +	/* drain rx bytes until empty */
>> +	for (;;) {
>> +		sr = readl(pic32s->regs + SPISTAT);
>> +		if (sr & STAT_RF_EMPTY)
>> +			break;
>> +
>> +		(void)readl(pic32s->regs + SPIBUF);
> Why do you need this cast to void?

Will drop.

>> +	}
> A busy waiting loop like this is more where I'd expect to see a
> cpu_relax().  I'd also expect to see some kind of timeout here,
> otherwise if something goes wrong we could lock up.

Will add usleep_range() and timeout check to avoid unbounded wait.

>> +static inline void spi_set_clk_rate(struct pic32_spi *pic32s, u32 sck)
> Essentially all the functions in this file appear to be marked as
> inline.  Don't do this unless the function really *needs* to be inline,
> just let the compiler inline it if it figures out that it's a good idea.

Will remove 'inline' keyword in larger functions.
Also as per my understanding compiler ignores 'inline' hint if it finds otherwise.

>> +static inline void spi_set_ss_auto(struct pic32_spi *pic32s, u8 mst, u32 mode)
>> +{
>> +	u32 v;
>> +
>> +	/* spi controller can drive CS/SS during transfer depending on fifo
>> +	 * fill-level. SS will stay asserted as long as TX fifo has something
>> +	 * to transfer, else will be deasserted confirming completion of
>> +	 * the ongoing transfer.
>> +	 */
>> +
>> +	v = readl(pic32s->regs + SPICON);
>> +	v &= ~SPICON_MSSEN;
>> +	if (mst) {
>> +		v |= SPICON_MSSEN;
>> +		if (mode & SPI_CS_HIGH)
>> +			v |= SPICON_FRMPOL;
>> +		else
>> +			v &= ~SPICON_FRMPOL;
>> +	}
>> +
>> +	writel(v, pic32s->regs + SPICON);
>> +}
> I don't really know what the above is suposed to do just from looking at
> it.  If it's enabling automatic /CS managment that doesn't sound like
> something we can actually use in Linux based on the comment.

The functions enables/disables automatic /CS management depending on 'mst'
argument which is govern by presence of valid cs_gpio.
Now we know, clearly, the SPI IP works correct only with GPIO controlled
/CS management. So will remove this logic and force disable-automatic /CS  handling.

>> +static inline void spi_set_err_int(struct pic32_spi *pic32s)
>> +{
>> +	u32 mask;
>> +
>> +	mask = SPI_INT_TX_UR_EN | SPI_INT_RX_OV_EN | SPI_INT_FRM_ERR_EN;
>> +	writel(mask, pic32s->regs + SPICON2_SET);
>> +}
> There is no need for this to be a function - there is one caller and
> it contains only a single function.  Just inline it and add a comment if
> there is a need for documentation.  This applies to quite a lot of the
> functions in this file, they are very small and have only one user so
> mostly just make the code less direct.  Using spi_ as the prefix also
> has a namespacing issue, that's the namespace for the core.

ack. Will replace accordingly.

>> +	pic32s->mesg->state = (void *)-1;
> This is trying to munge a numeric return code into a pointer without
> using PTR_ERR() and friends which is ugly and fragile.  If you really
> need to do this use the standard macros, but since we already have an
> error code in the message you can use that (though it seems nothing
> actually ever reads these...).  You should also use real error codes not
> magic numbers.

Ack, Will implement transfer_one() and there will be no need of handling
message state at all.

>> +	complete(&pic32s->xfer_done);
>> +
>> +	disable_irq_nosync(pic32s->fault_irq);
>> +	disable_irq_nosync(pic32s->rx_irq);
>> +	disable_irq_nosync(pic32s->tx_irq);
> This is racy, you are completing the transfer then disabling the
> interrupts.  Something could come along and try and do another transfer
> before the interrupts are disabled.

Good catch. Will change the order.

>> +	if (!pic32s->mesg) {
>> +		pic32_err_stop(pic32s, "err_irq: mesg error");
>> +		goto irq_handled;
>> +	}
> There's nothing in this case that checks that the interrupt actually
> fired.

ack. Will return with IRQ_NONE in this case.

>> +	/* tx complete? mask and disable tx interrupt */
>> +	if (pic32s->tx_end == pic32s->tx)
>> +		disable_irq_nosync(pic32s->tx_irq);
> It seems there's no interrupt masking in the actual IP and the
> interrupts will scream when the IP is idle?
>
At IP level there is no interrupt masking capability. So to disable
firing interrupt when IP is idle interrupts are masked/disabled at
interrupt controller level. 

>> +static inline void pic32_spi_cs_assert(struct pic32_spi *pic32s)
>> +{
>> +	int cs_high;
>> +	struct spi_device *spi_dev = pic32s->spi_dev;
>> +
>> +	if (pic32s->flags & SPI_SS_MASTER)
>> +		return;
>> +
>> +	cs_high = pic32s->mode & SPI_CS_HIGH;
>> +	gpio_set_value(spi_dev->cs_gpio, cs_high);
>> +}
> Don't open code GPIO chip selects, use the core support.

ack. Will implement .transfer_one() callback and use SPI core support.

>> +static void pic32_spi_dma_rx_notify(void *data)
>> +{
>> +	struct pic32_spi *pic32s = data;
>> +
>> +	spin_lock(&pic32s->lock);
>> +	complete(&pic32s->xfer_done);
>> +	spin_unlock(&pic32s->lock);
>> +}
> Taking the spinlock here looks completely pointless - what is it
> intended to protect?

Will drop.

>> +err_dma:
>> +	pic32_spi_dma_abort(pic32s);
>> +	return -ENOMEM;
> -ENOMEM looks completely random here, please use a sensible error code
> (if you got one back from another funtion pass it through).

ack. Will use same error code as returned by failed function call.

>> +static int pic32_spi_one_transfer(struct pic32_spi *pic32s,
>> +				  struct spi_message *message,
>> +				  struct spi_transfer *transfer)
>> +	if (transfer->speed_hz && (transfer->speed_hz != pic32s->speed_hz)) {
> Just use the transfer, the core will ensure that it is set.

ack.

>> +	spin_lock_irqsave(&pic32s->lock, flags);
>> +
>> +	spi_enable_chip(pic32s);
>> +
>> +	/* polling mode? */
>> +	if (pic32s->flags & SPI_XFER_POLL) {
>> +		ret = pic32_spi_poll_transfer(pic32s, 2 * HZ);
>> +		spin_unlock_irqrestore(&pic32s->lock, flags);
>> +
>> +		if (ret) {
>> +			dev_err(&master->dev, "poll-xfer timedout\n");
>> +			message->status = ret;
>> +			goto err_xfer_done;
>> +		}
>> +		goto out_xfer_done;
>> +	}
>> +
>> +	reinit_completion(&pic32s->xfer_done);
>> +
>> +	/* DMA mode ? */
>> +	if (pic32_spi_dma_is_ready(pic32s)) {
>> +		spin_unlock_irqrestore(&pic32s->lock, flags);
>> +
>> +		ret = pic32_spi_dma_transfer(pic32s, transfer);
>> +		if (ret) {
>> +			dev_err(&master->dev, "dma xfer error\n");
>> +			message->status = ret;
>> +			spin_lock_irqsave(&pic32s->lock, flags);
>> +		} else {
>> +			goto out_wait_for_xfer;
>> +		}
>> +	}
>> +
>> +	/* enable interrupt */
>> +	enable_irq(pic32s->fault_irq);
>> +	enable_irq(pic32s->tx_irq);
>> +	enable_irq(pic32s->rx_irq);
>> +
>> +	spin_unlock_irqrestore(&pic32s->lock, flags);
> This seems like a very large section of code to hold a spinlock for and
> I'm not immediately seeing a reason why the locking has to be so
> aggressive.  Among other things it's holding a spinlock with interrupts
> disabled for up to two seconds over a polling transfer which is at best
> needless.

ack. Will remove locking requirement for polling-mode (needed to support
automatic /CS handling).

>> +static int pic32_spi_one_message(struct spi_master *master,
>> +				 struct spi_message *msg)
>> +{
>> +	int ret = 0;
>> +	int cs_active = 0;
> Don't open code message parsing, use the core support and implement
> transfer_one().

ack. Will implement.

>> +	clk_prepare_enable(pic32s->clk);
> No error checking.  It'd also be better to have runtime power management
> of this.

Will add error checking. Currently we don't have support for runtime power-management.

>> +	if (dev->of_node) {
> This has DT support but the DT binding is not documented.  Documentation
> is mandatory for all new DT bindings.

ack. See above for DT documentation.

>> +		of_property_read_u32(dev->of_node,
>> +				     "max-clock-frequency", &max_spi_rate);
> This looks like it's duplicating something that should be in the clock
> bindings.  As far as I can tell we never change the parent clock rate so
> we can just look at that to identify the maximum clock rate.

ack. Will drop this and derive maximum clock rate from the parent clock.

>> +		if (of_find_property(dev->of_node, "use-no-dma", NULL)) {
>> +			dev_warn(dev, "DMA support not requested\n");
>> +			pic32s->flags &= ~SPI_DMA_CAP;
>> +		}
> Why not just handle the DT binding information being missing?

Will drop this DT property (added mainly for debug purpose).