linux-kernel - Re: [PATCH] usb:serial: Add Fintek F81532/534 driver

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Message-ID: <af06aa19-faa9-8d17-95cd-565bdf2f82b1@gmail.com>
Date:	Thu, 4 Aug 2016 14:25:24 +0800
From:	"Ji-Ze Hong (Peter Hong)" <hpeter@...il.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	johan@...nel.org, gregkh@...uxfoundation.org,
	tom_tsai@...tek.com.tw, peter_hong@...tek.com.tw,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Ji-Ze Hong (Peter Hong)" <hpeter+linux_kernel@...il.com>
Subject: Re: [PATCH] usb:serial: Add Fintek F81532/534 driver

Hi Alan,

One Thousand Gnomes 於 2016/7/29 下午 08:48 寫道:
> O
>> +static int f81534_set_normal_register(struct usb_device *dev, u16 reg, u8 data)
>> +{
>> +	size_t count = F81534_USB_MAX_RETRY;
>> +	int status;
>> +	u8 *tmp;
>> +
>> +	tmp = kmalloc(sizeof(u8), GFP_KERNEL);
>> +	if (!tmp)
>> +		return -ENOMEM;
>
> You end up doing huge numbers of tiny allocation and frees in some of the
> code paths. I think it would be better to allocate them at a higher level
> as they are not that cheap on CPU time.
>
>> +static int f81534_read_data(struct usb_serial *usbserial, u32 address,
>> +				size_t size, unsigned char *buf)
>> +{
>
> Is a particularly good example - you do 4 mallocs plus two per byte of
> data.
>

I'll re-factor the newest V9 patch with your suggestion. To malloc a
byte within usb_serial privates, and make a mutex to protect it.

I'll send it as V10 when I tested it.

Thanks for your suggestion.
-- 
With Best Regards,
Peter Hong