linux-kernel - Re: [PATCH v3 2/7] mmc: sdhci: add support for using external DMA devices

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Date:   Mon, 23 Dec 2019 19:55:22 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-mmc@...r.kernel.org>
CC:     <kishon@...com>, <mark.rutland@....com>, <robh+dt@...nel.org>,
        <ulf.hansson@...aro.org>, <zhang.chunyan@...aro.org>,
        <tony@...mide.com>
Subject: Re: [PATCH v3 2/7] mmc: sdhci: add support for using external DMA
 devices

Hi Adrian,

On 16/12/19 7:15 pm, Adrian Hunter wrote:
> On 16/12/19 10:27 am, Faiz Abbas wrote:
>> Hi Adrian,
>>
>> On 12/12/19 6:25 pm, Adrian Hunter wrote:
>>> On 10/12/19 11:51 am, Faiz Abbas wrote:
>>>> From: Chunyan Zhang <zhang.chunyan@...aro.org>
>>>>
>>>> Some standard SD host controllers can support both external dma
>>>> controllers as well as ADMA/SDMA in which the SD host controller
>>>> acts as DMA master. TI's omap controller is the case as an example.
>>>>
>>>> Currently the generic SDHCI code supports ADMA/SDMA integrated in
>>>> the host controller but does not have any support for external DMA
>>>> controllers implemented using dmaengine, meaning that custom code is
>>>> needed for any systems that use an external DMA controller with SDHCI.
>>>>
>>>> Fixes by Faiz Abbas <faiz_abbas@...com>:
>>>> 1. Map scatterlists before dmaengine_prep_slave_sg()
>>>> 2. Use dma_async() functions inside of the send_command() path and call
>>>> terminate_sync() in non-atomic context in case of an error.
>>>>
>>>> @@ -2652,6 +2845,18 @@ static bool sdhci_request_done(struct sdhci_host *host)
>>>>  	if (host->flags & SDHCI_REQ_USE_DMA) {
>>>>  		struct mmc_data *data = mrq->data;
>>>>  
>>>> +		spin_unlock_irqrestore(&host->lock, flags);
>>>> +
>>>> +		/* Terminate and synchronize dma in case of an error */
>>>> +		if (data && (mrq->cmd->error || data->error) &&
>>>> +		    host->use_external_dma) {
>>>> +			struct dma_chan *chan = sdhci_external_dma_channel(host,
>>>> +									  data);
>>>> +			dmaengine_terminate_sync(chan);
>>>> +		}
>>>> +
>>>> +		spin_lock_irqsave(&host->lock, flags);
>>>> +
>>>
>>> Need to take the mrq out of mrqs_done[] to ensure it is not processed again,
>>> and put it back again to be consistent with the remaining code. Also put
>>> host->use_external_dma as the first condition i.e.
>>>
>>> 		if (host->use_external_dma && data &&
>>> 		    (mrq->cmd->error || data->error)) {
>>> 			struct dma_chan *chan = sdhci_external_dma_channel(host, data);
>>>
>>> 			host->mrqs_done[i] = NULL;
>>> 			spin_unlock_irqrestore(&host->lock, flags);
>>> 			dmaengine_terminate_sync(chan);
>>> 			spin_lock_irqsave(&host->lock, flags);
>>> 			sdhci_set_mrq_done(host, mrq);
>>> 		}
>>>
>>> where sdhci_set_mrq_done() is factored out from __sdhci_finish_mrq() i.e.
>>>
>>> static void sdhci_set_mrq_done(struct sdhci_host *host, struct mmc_request *mrq)
>>> {
>>> 	int i;
>>>
>>> 	for (i = 0; i < SDHCI_MAX_MRQS; i++) {
>>> 		if (host->mrqs_done[i] == mrq) {
>>> 			WARN_ON(1);
>>> 			return;
>>> 		}
>>> 	}
>>>
>>> 	for (i = 0; i < SDHCI_MAX_MRQS; i++) {
>>> 		if (!host->mrqs_done[i]) {
>>> 			host->mrqs_done[i] = mrq;
>>> 			break;
>>> 		}
>>> 	}
>>>
>>> 	WARN_ON(i >= SDHCI_MAX_MRQS);
>>> }
>>>
>>> sdhci_set_mrq_done() can be made in the refactoring patch.
>> Haven't we already done the sdhci_set_mrq_done() part in
>> __sdhci_finish_mrq()?
>>
>> We are picking up an already "done" mrq, looking at whether it had any
>> error and then sychronizing with external dma. Or at least that is my
>> understanding.
> 
> sdhci supports having 2 requests (1 data, 1 cmd) at a time, so there is an
> error case where 1 request will wait for the 2nd request before doing a
> reset.  That logic is further down in sdhci_request_done() so you have to
> put the mrq back into host->mrqs_done[] to make it work.

Sorry for the late response. I had to spend some time figuring out how
the mrqs_done handling works. Will add the new function above.

> 
>>
>>>
>>>>  		if (data && data->host_cookie == COOKIE_MAPPED) {
>>>>  			if (host->bounce_buffer) {
>>>>  				/*
>>>> @@ -3758,12 +3963,28 @@ int sdhci_setup_host(struct sdhci_host *host)
>>>>  		       mmc_hostname(mmc), host->version);
>>>>  	}
>>>>  
>>>> -	if (host->quirks & SDHCI_QUIRK_FORCE_DMA)
>>>> +	if (host->use_external_dma) {
>>>> +		ret = sdhci_external_dma_init(host);
>>>> +		if (ret == -EPROBE_DEFER)
>>>> +			goto unreg;
>>>> +
>>>> +		/*
>>>> +		 * Fall back to use the DMA/PIO integrated in standard SDHCI
>>>> +		 * instead of external DMA devices.
>>>> +		 */
>>>> +		if (ret)
>>>> +			sdhci_switch_external_dma(host, false);
>>>> +	}
>>>> +
>>>> +	if (host->quirks & SDHCI_QUIRK_FORCE_DMA) {
>>>>  		host->flags |= SDHCI_USE_SDMA;
>>>> -	else if (!(host->caps & SDHCI_CAN_DO_SDMA))
>>>> +	} else if (!(host->caps & SDHCI_CAN_DO_SDMA)) {
>>>>  		DBG("Controller doesn't have SDMA capability\n");
>>>> -	else
>>>> +	} else if (host->use_external_dma) {
>>>> +		/* Using dma-names to detect external dma capability */
>>>
>>> What is this change for?  Do you expect for SDHCI_USE_SDMA and
>>> SDHCI_USE_ADMA flags to be clear?
>>
>> Yes. Today the code enables SDMA by default (in the else part below
>> this). I want it to not enable SDMA in the external dma case.
> 
> What about moving the "if (host->use_external_dma) {" clause and explicitly
> clearing SDHCI_USE_SDMA and SDHCI_USE_ADMA?
> 

I am ok with this as well. Sending a new version.

Thanks,
Faiz