linux-kernel - Re: [PATCH v5 2/5] USB: use genalloc for USB HCs with local memory

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Date:   Wed, 22 May 2019 10:45:35 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Alan Stern <stern@...land.harvard.edu>
CC:     "hch@....de" <hch@....de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "marex@...x.de" <marex@...x.de>, Leo Li <leoyang.li@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "noring@...rew.org" <noring@...rew.org>,
        "JuergenUrban@....de" <JuergenUrban@....de>
Subject: Re: [PATCH v5 2/5] USB: use genalloc for USB HCs with local memory

Hello Alan,

On 21.05.2019 20:20, Alan Stern wrote:
> On Tue, 21 May 2019 laurentiu.tudor@....com wrote:
> 
>> From: Laurentiu Tudor <laurentiu.tudor@....com>
>>
>> For HCs that have local memory, replace the current DMA API usage
>> with a genalloc generic allocator to manage the mappings for these
>> devices. To help users, introduce a new HCD API,
>> usb_hcd_setup_local_mem() that will setup up the genalloc backing
>> up the device local memory. It will be used in subsequent patches.
>> This is in preparation for dropping the existing "coherent" dma
>> mem declaration APIs. Current implementation was relying on a short
>> circuit in the DMA API that in the end, was acting as an allocator
>> for these type of devices.
>>
>> For context, see thread here: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org%2Flkml%2F2019%2F4%2F22%2F357&amp;data=02%7C01%7Claurentiu.tudor%40nxp.com%7Cdc4a76b04b874b75bd5408d6de109d86%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636940560281957207&amp;sdata=JQ1iJc%2Fw%2BwHdTFvaOT%2FYHBx%2BVQlpHWlf346q7sclfcg%3D&amp;reserved=0
>>
>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@....com>
>> Signed-off-by: Fredrik Noring <noring@...rew.org>
>> ---
> 
>> --- a/drivers/usb/core/hcd.c
>> +++ b/drivers/usb/core/hcd.c
>> @@ -29,6 +29,8 @@
>>   #include <linux/workqueue.h>
>>   #include <linux/pm_runtime.h>
>>   #include <linux/types.h>
>> +#include <linux/genalloc.h>
>> +#include <linux/io.h>
>>   
>>   #include <linux/phy/phy.h>
>>   #include <linux/usb.h>
>> @@ -3039,6 +3041,40 @@ usb_hcd_platform_shutdown(struct platform_device *dev)
>>   }
>>   EXPORT_SYMBOL_GPL(usb_hcd_platform_shutdown);
>>   
>> +int usb_hcd_setup_local_mem(struct usb_hcd *hcd, phys_addr_t phys_addr,
>> +			    dma_addr_t dma, size_t size)
>> +{
>> +	int err;
>> +	void __iomem *local_mem;
>> +
>> +	hcd->localmem_pool = devm_gen_pool_create(hcd->self.sysdev, PAGE_SHIFT,
>> +						  dev_to_node(hcd->self.sysdev),
>> +						  "ohci-hcd");
> 
> Surely that string is a mistake.  You could use
> dev_name(hcd->self.sysdev) or a name passed by the caller.

Sorry, missed that. Will go with dev_name() if that's ok with you.

>> +	if (IS_ERR(hcd->localmem_pool))
>> +		return PTR_ERR(hcd->localmem_pool);
>> +
>> +	local_mem = devm_memremap(hcd->self.sysdev, phys_addr,
>> +				  size, MEMREMAP_WC);
>> +	if (!local_mem)
>> +		return -ENOMEM;
>> +
>> +	/*
>> +	 * Here we pass a dma_addr_t but the arg type is a phys_addr_t.
>> +	 * It's not backed by system memory and thus there's no kernel mapping
>> +	 * for it.
>> +	 */
>> +	err = gen_pool_add_virt(hcd->localmem_pool, (unsigned long)local_mem,
>> +				dma, size, dev_to_node(hcd->self.sysdev));
>> +	if (err < 0) {
>> +		dev_err(hcd->self.sysdev, "gen_pool_add_virt failed with %d\n",
>> +			err);
>> +		return err;
>> +	}
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(usb_hcd_setup_local_mem);
> 
> If you have a usb_hcd_setup_local_mem() function then you should also
> have a usb_hcd_remove_local_mem() function.

Even if all resources that are allocated are device managed?

>> --- a/drivers/usb/host/ohci-mem.c
>> +++ b/drivers/usb/host/ohci-mem.c
>> @@ -36,6 +36,12 @@ static void ohci_hcd_init (struct ohci_hcd *ohci)
>>   
>>   static int ohci_mem_init (struct ohci_hcd *ohci)
>>   {
>> +	if (ohci_to_hcd(ohci)->localmem_pool) {
>> +		ohci->td_cache = NULL;
>> +		ohci->ed_cache = NULL;
>> +		return 0;
>> +	}
> 
> This really isn't necessary.  The entire ohci_hcd structure is
> initialized to 0 when it is first allocated.

Will drop.

>> --- a/include/linux/usb/hcd.h
>> +++ b/include/linux/usb/hcd.h
>> @@ -216,6 +216,9 @@ struct usb_hcd {
>>   #define	HC_IS_RUNNING(state) ((state) & __ACTIVE)
>>   #define	HC_IS_SUSPENDED(state) ((state) & __SUSPEND)
>>   
>> +	/* allocator for HCs having local memory */
> 
> "allocator" is the wrong word -- an allocator is something that
> allocates.  Perhaps "memory area" or something along those lines.

Alright, I will rework.

---
Thanks & Best Regards, Laurentiu