[RFC PATCH] mmc: sdhci-of-arasan: Add auto tuning support for ZynqMP Platform

[adrian.hunter@intel.com (Adrian Hunter)]

On 23/02/18 09:29, Manish Narani wrote:
> 
> 
>> -----Original Message-----
>> From: Adrian Hunter [mailto:adrian.hunter at intel.com]
>> Sent: Thursday, February 22, 2018 1:50 PM
>> To: Manish Narani <MNARANI@xilinx.com>; michal.simek at xilinx.com;
>> ulf.hansson at linaro.org; linux-arm-kernel at lists.infradead.org; linux-
>> mmc at vger.kernel.org; linux-kernel at vger.kernel.org;
>> devicetree at vger.kernel.org; mark.rutland at arm.com; robh+dt at kernel.org
>> Cc: Anirudha Sarangi <anirudh@xilinx.com>; Srinivas Goud
>> <sgoud@xilinx.com>
>> Subject: Re: [RFC PATCH] mmc: sdhci-of-arasan: Add auto tuning support for
>> ZynqMP Platform
>>
>> On 21/02/18 17:00, Manish Narani wrote:
>>> Hi Adrian,
>>>
>>>> -----Original Message-----
>>>> From: Manish Narani
>>>> Sent: Wednesday, February 21, 2018 11:39 AM
>>>> To: Adrian Hunter <adrian.hunter@intel.com>; michal.simek at xilinx.com;
>>>> ulf.hansson at linaro.org; linux-arm-kernel at lists.infradead.org; linux-
>>>> mmc at vger.kernel.org; linux-kernel at vger.kernel.org;
>>>> devicetree at vger.kernel.org; mark.rutland at arm.com;
>> robh+dt at kernel.org
>>>> Cc: Anirudha Sarangi <anirudh@xilinx.com>; Srinivas Goud
>>>> <sgoud@xilinx.com>
>>>> Subject: RE: [RFC PATCH] mmc: sdhci-of-arasan: Add auto tuning
>>>> support for ZynqMP Platform
>>>>
>>>> Hi Adrian,
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Adrian Hunter [mailto:adrian.hunter at intel.com]
>>>>> Sent: Friday, February 16, 2018 7:37 PM
>>>>> To: Manish Narani <MNARANI@xilinx.com>; michal.simek at xilinx.com;
>>>>> ulf.hansson at linaro.org; linux-arm-kernel at lists.infradead.org; linux-
>>>>> mmc at vger.kernel.org; linux-kernel at vger.kernel.org;
>>>>> devicetree at vger.kernel.org; mark.rutland at arm.com;
>> robh+dt at kernel.org
>>>>> Cc: Anirudha Sarangi <anirudh@xilinx.com>; Srinivas Goud
>>>>> <sgoud@xilinx.com>; Manish Narani <MNARANI@xilinx.com>
>>>>> Subject: Re: [RFC PATCH] mmc: sdhci-of-arasan: Add auto tuning
>>>>> support for ZynqMP Platform
>>>>>
>>>>> On 30/01/18 20:14, Manish Narani wrote:
>>>>>> This patch adds support of SD auto tuning for ZynqMP platform. Auto
>>>>>> tuning sequence sends tuning block to card when operating in UHS-1
>>>>>> modes. This resets the DLL and sends CMD19/CMD21 as a part of the
>>>>>> auto tuning process. Once the auto tuning process gets completed,
>>>>>> reset the DLL to load the newly obtained SDHC tuned tap value.
>>>>>
>>>>> How is this different from:
>>>>> 	1. reset the dll
>>>>> 	2. call sdhci_execute_tuning
>>>>> 	3. reset the dll
>>>>>
>>> Below is my take on your above comments:
>>> - 'Reset the dll' is a platform specific call inside
>>> 'arasan_zynqmp_execute_tuning' which is implemented in
>>> sdhci-of-arasan.c
>>> - 'arasan_zynqmp_execute_tuning' is called from 'sdhci_execute_tuning'
>>> as a platform_execute_tuning routine
>>> - So to keep 'DLL reset' routine called from sdhci-of-arasan.c, I have
>>> implemented the execute_tuning in sdhci-of-arasan.c
>>
>> I meant something like:
>>
>> 	if (of_device_is_compatible(pdev->dev.of_node, "xlnx,zynqmp-
>> 8.9a"))
>> 		host->mmc_host_ops.execute_tuning =
>> arasan_zynqmp_execute_tuning;
>>
> This will need the removal of 'const' from 'static const struct mmc_host_ops sdhci_ops = {}' in sdhci.c file. Please confirm.

No, it is not const.  You are not looking at the right place. i.e.

$ grep mmc_host_ops drivers/mmc/host/sdhci.h
        struct mmc_host_ops mmc_host_ops;       /* MMC host ops */

> 
> Thanks,
> Manish
>>
>> static int arasan_zynqmp_execute_tuning(struct mmc_host *mmc, u32
>> opcode) {
>> 	struct sdhci_host *host = mmc_priv(mmc);
>> 	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>> 	struct sdhci_arasan_data *sdhci_arasan =
>> sdhci_pltfm_priv(pltfm_host);
>> 	int err;
>>
>> 	arasan_zynqmp_dll_reset(host, sdhci_arasan->device_id);
>>
>> 	err = sdhci_execute_tuning(mmc, opcode);
>> 	if (err)
>> 		return err;
>>
>> 	arasan_zynqmp_dll_reset(host, sdhci_arasan->device_id);
>>
>> 	return 0;
>> }
>>
>>>
>>> Alternative way (Please review):
>>> - Define a host->quirk2 bit (SDHCI_QUIRK2_DLL_RESET_NEEDED) in
>>> sdhci-of-arasan.c indicating DLL reset needed while tuning operation
>>> - Call 'dll reset' routine before and after __sdhci_execute_tuning()
>>> in sdhci.c when a host->quirk2 bit (SDHCI_QUIRK2_DLL_RESET_NEEDED) is
>>> set
>>
>> We should try to avoid quirks.