Subject: [PATCH v1 03/11] drivers: soc: hisi: Add support for Hisilicon Djtag driver

From: [email-masked] (Anurup M)
Date: Tue, 8 Nov 2016 13:08:31 +0530

On Tuesday 08 November 2016 12:32 PM, Tan Xiaojun wrote:
> On 2016/11/7 21:26, Arnd Bergmann wrote:
>> On Wednesday, November 2, 2016 11:42:46 AM CET Anurup M wrote:
>>> From: Tan Xiaojun <[email-masked]>
>>>
>>> 	The Hisilicon Djtag is an independent component which connects
>>> 	with some other components in the SoC by Debug Bus. This driver
>>> 	can be configured to access the registers of connecting components
>>> 	(like L3 cache) during real time debugging.
>> The formatting of the text seems odd, please remove the leading spaces.
>>
> Sorry for that. We will fix it.
>
>>>   drivers/soc/Kconfig                 |   1 +
>>>   drivers/soc/Makefile                |   1 +
>>>   drivers/soc/hisilicon/Kconfig       |  12 +
>>>   drivers/soc/hisilicon/Makefile      |   1 +
>>>   drivers/soc/hisilicon/djtag.c       | 639 ++++++++++++++++++++++++++++++++++++
>>>   include/linux/soc/hisilicon/djtag.h |  38 +++
>> Do you expect other drivers to be added that reference this interface?
>> If not, or if you are unsure, just put all of it under drivers/perf
>> so we don't introduce a global API that has only one user.
>>
> OK. For now, this suggestion sounds good.
>
>>> +
>>> +#include <linux/bitops.h>
>>> +#include <linux/init.h>
>>> +#include <linux/list.h>
>>> +#include <linux/module.h>
>>> +#include <linux/of.h>
>>> +#include <linux/of_address.h>
>>> +#include <linux/of_device.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/spinlock.h>
>>> +
>>> +#include <asm-generic/delay.h>
>> Never include files from asm-generic directly except from
>> an architecture specific asm/*.h header file.
>>
>>
> OK. Sorry for that.
>
>>> +DEFINE_IDR(djtag_hosts_idr);
>> make this static
>>
> OK.
>
>>> +static void djtag_read32_relaxed(void __iomem *regs_base, u32 off, u32 *value)
>>> +{
>>> +	void __iomem *reg_addr = regs_base + off;
>>> +
>>> +	*value = readl_relaxed(reg_addr);
>>> +}
>>> +
>>> +static void djtag_write32(void __iomem *regs_base, u32 off, u32 val)
>>> +{
>>> +	void __iomem *reg_addr = regs_base + off;
>>> +
>>> +	writel(val, reg_addr);
>>> +}
>> This looks like an odd combination of interfaces.
>> Why can the reads be "relaxed" when the writes can not?
>>
>> Generally speaking, I'd advise to always use non-relaxed accessors
>> unless there is a strong performance reason, and in that case there
>> should be a comment explaining the use at each of the callers
>> of a relaxed accessor.
>>
> Yes, it is our mistake.
Shall use non-relaxed version and make it consistent.
>>> +	/* ensure the djtag operation is done */
>>> +	do {
>>> +		djtag_read32_relaxed(regs_base, SC_DJTAG_MSTR_START_EN_EX, &rd);
>>> +
>>> +		if (!(rd & DJTAG_MSTR_START_EN_EX))
>>> +			break;
>>> +
>>> +		udelay(1);
>>> +	} while (timeout--);
>> This one is obviously not performance critical at all, so use a non-relaxed
>> accessor. Same for the other two in this function.
>>
>> Are these functions ever called from atomic context? If yes, please document
>> from what context they can be called, otherwise please consider changing
>> the udelay calls into sleeping waits.
>>
> Yes, this is not reentrant.
The read/write functions shall also be called from irq handler (for 
handling counter overflow).
So need to use udelay calls. Shall Document it in v2.
>>> +int hisi_djtag_writel(struct hisi_djtag_client *client, u32 offset, u32 mod_sel,
>>> +							u32 mod_mask, u32 val)
>>> +{
>>> +	void __iomem *reg_map = client->host->sysctl_reg_map;
>>> +	unsigned long flags;
>>> +	int ret = 0;
>>> +
>>> +	spin_lock_irqsave(&client->host->lock, flags);
>>> +	ret = client->host->djtag_readwrite(reg_map, offset, mod_sel, mod_mask,
>>> +					true, val, 0, NULL);
>>> +	if (ret)
>>> +		pr_err("djtag_writel: error! ret=%d\n", ret);
>>> +	spin_unlock_irqrestore(&client->host->lock, flags);
>>> +
>>> +	return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(hisi_djtag_writel);
>> That would of course imply changing the spinlock to a mutex here as well.
>>
>>> +static const struct of_device_id djtag_of_match[] = {
>>> +	/* for hip05(D02) cpu die */
>>> +	{ .compatible = "hisilicon,hip05-cpu-djtag-v1",
>>> +		.data = (void *)djtag_readwrite_v1 },
>>> +	/* for hip05(D02) io die */
>>> +	{ .compatible = "hisilicon,hip05-io-djtag-v1",
>>> +		.data = (void *)djtag_readwrite_v1 },
>>> +	/* for hip06(D03) cpu die */
>>> +	{ .compatible = "hisilicon,hip06-cpu-djtag-v1",
>>> +		.data = (void *)djtag_readwrite_v1 },
>>> +	/* for hip06(D03) io die */
>>> +	{ .compatible = "hisilicon,hip06-io-djtag-v2",
>>> +		.data = (void *)djtag_readwrite_v2 },
>>> +	/* for hip07(D05) cpu die */
>>> +	{ .compatible = "hisilicon,hip07-cpu-djtag-v2",
>>> +		.data = (void *)djtag_readwrite_v2 },
>>> +	/* for hip07(D05) io die */
>>> +	{ .compatible = "hisilicon,hip07-io-djtag-v2",
>>> +		.data = (void *)djtag_readwrite_v2 },
>>> +	{},
>>> +};
>> If these are backwards compatible, just mark them as compatible in DT,
>> e.g. hip06 can use
>>
>> 	compatible = "hisilicon,hip06-cpu-djtag-v1", "hisilicon,hip05-cpu-djtag-v1";
>>
>> so you can tell the difference if you need to, but the driver only has to
>> list the oldest one here.
>>
>> What is the difference between the cpu and io djtag interfaces?
On some chips like hip06, the djtag version is different for IO die.

Thanks,
Anurup
>>
>> I think you can also drop the '(void *)'.
>>
> OK. We will consider it.
>
> Thanks.
> Xiaojun.
>
>>> +static void djtag_register_devices(struct hisi_djtag_host *host)
>>> +{
>>> +	struct device_node *node;
>>> +	struct hisi_djtag_client *client;
>>> +
>>> +	if (!host->of_node)
>>> +		return;
>>> +
>>> +	for_each_available_child_of_node(host->of_node, node) {
>>> +		if (of_node_test_and_set_flag(node, OF_POPULATED))
>>> +			continue;
>>> +		client = hisi_djtag_of_register_device(host, node);
>>> +		list_add(&client->next, &host->client_list);
>>> +	}
>>> +}
>> Can you explain your thoughts behind creating a new bus type
>> and adding the child devices manually rather than using
>> platform_device structures with of_platform_populate()?
>>
>> Do you expect to see other implementations of this bus type
>> with incompatible bus drivers?
>>
>> 	Arnd
>>
>>
>> .
>>
>