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Mon, 10 Feb 2020 20:05:19 +0000 Received: from b03ledav003.gho.boulder.ibm.com (b03ledav003.gho.boulder.ibm.com [9.17.130.234]) by b03cxnp07028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01AK5IWZ43188664 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 10 Feb 2020 20:05:18 GMT Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 298256A047; Mon, 10 Feb 2020 20:05:18 +0000 (GMT) Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id ABCD66A04D; Mon, 10 Feb 2020 20:05:17 +0000 (GMT) Received: from [9.41.103.158] (unknown [9.41.103.158]) by b03ledav003.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 10 Feb 2020 20:05:17 +0000 (GMT) Subject: Re: [PATCH] spi: Add FSI-attached SPI controller driver To: Andy Shevchenko Cc: Eddie James , linux-spi , Linux Kernel Mailing List , Mark Brown , Joel Stanley , Andrew Jeffery References: <1580328504-436-1-git-send-email-eajames@linux.ibm.com> <29f6cc86-69ca-bc88-b6ae-2b1a24c0dae3@linux.vnet.ibm.com> <744f0019-8656-eec1-cb9a-7e70cd042587@linux.ibm.com> <90973143-bd0a-33cf-9eb8-a83be1a9b415@linux.vnet.ibm.com> From: Eddie James Message-ID: <3bbc98a7-838d-f57f-0478-a632ba68f500@linux.vnet.ibm.com> Date: Mon, 10 Feb 2020 14:05:17 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-10_07:2020-02-10,2020-02-10 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 bulkscore=0 spamscore=0 impostorscore=0 lowpriorityscore=0 mlxscore=0 suspectscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002100147 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/7/20 4:04 PM, Andy Shevchenko wrote: > On Fri, Feb 7, 2020 at 11:04 PM Eddie James wrote: >> On 2/7/20 2:34 PM, Andy Shevchenko wrote: >>> On Fri, Feb 7, 2020 at 10:04 PM Eddie James wrote: >>>> On 2/7/20 1:39 PM, Andy Shevchenko wrote: >>>>> On Fri, Feb 7, 2020 at 9:28 PM Eddie James wrote: >>>>>> On 2/5/20 9:51 AM, Andy Shevchenko wrote: >>>>>>> On Tue, Feb 4, 2020 at 6:06 PM Eddie James wrote: >>>>>>>> On 2/4/20 5:02 AM, Andy Shevchenko wrote: >>>>>>>>> On Mon, Feb 3, 2020 at 10:33 PM Eddie James wrote: >>>>>>>>>> On 1/30/20 10:37 AM, Andy Shevchenko wrote: >>>>>>>>>>>> + for (i = 0; i < num_bytes; ++i) >>>>>>>>>>>> + rx[i] = (u8)((in >> (8 * ((num_bytes - 1) - i))) & 0xffULL); >>>>>>>>>>> Redundant & 0xffULL part. >>>>>>> For me it looks like >>>>>>> >>>>>>> u8 tmp[8]; >>>>>>> >>>>>>> put_unaligned_be64(in, tmp); >>>>>>> memcpy(rx, tmp, num_bytes); >>>>>>> >>>>>>> put_unaligned*() is just a method to unroll the value to the u8 buffer. >>>>>>> See, for example, linux/unaligned/be_byteshift.h implementation. >>>>>> Unforunately it is not the same. put_unaligned_be64 will take the >>>>>> highest 8 bits (0xff00000000000000) and move it into tmp[0]. Then >>>>>> 0x00ff000000000000 into tmp[1], etc. This is only correct for this >>>>>> driver IF my transfer is 8 bytes. If, for example, I transfer 5 bytes, >>>>>> then I need 0x000000ff00000000 into tmp[0], 0x00000000ff000000 into >>>>>> tmp[1], etc. So I think my current implementation is correct. >>>>> Yes, I missed correction of the start address in memcpy(). Otherwise >>>>> it's still the same what I was talking about. >>>> I see now, yes, thanks. >>>> >>>> Do you think this is worth a v3? Perhaps put_unaligned is slightly more >>>> optimized than the loop but there is more memory copy with that way too. >>> I already forgot the entire context when this has been called. Can you >>> summarize what the sequence(s) of num_bytes are expected usually. >>> >>> IIUC if packets small, less than 8 bytes, than num_bytes will be that value. >>> Otherwise it will be something like 8 + 8 + 8 ... + tail. Is it >>> correct assumption? >> >> Yes, it will typically be 8 + 8 +... remainder. Basically, on any RX, >> the driver polls for the rx register full. Once full, it will read >> however much data is left to be transferred. Since we use min(len, 8) >> then we read 8 usually, until we get to the end. > I asked that because we might have a better optimization, i.e, call > directly put_unaligned_be64() when we know that length is 8 bytes. For > the rest your approach might be simpler. Similar for the TX case. I just tried to implement as you suggested but I realized something: The value is already swapped from BE to CPU when the register is read in fsi_spi_read_reg. It happens to work out correctly to use put_unaligned_be64 on a LE CPU to flip the bytes here. But on a BE CPU, this wouldn't be correct I think. Now I don't anticipate this driver running on a BE CPU, but I think it is weird to flip it twice, and better to do it manually here. What do you think Andy? Thanks, Eddie > >>>>>>>>>>>> + return num_bytes; >>>>>>>>>>>> +}