linux-kernel - Re: [PATCH V2 27/27] mmc: mmci: add stm32 sdmmc variant

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Date:   Mon, 1 Oct 2018 15:53:21 +0200
From:   Ludovic BARRE <ludovic.barre@...com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Gerald Baeza <gerald.baeza@...com>,
        Loic Pallardy <loic.pallardy@...com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH V2 27/27] mmc: mmci: add stm32 sdmmc variant



On 10/01/2018 03:39 PM, Ulf Hansson wrote:
> [...]
> 
>>>>    struct variant_data {
>>>>           unsigned int            clkreg;
>>>> @@ -348,6 +350,8 @@ struct variant_data {
>>>>           unsigned int            irq_pio_mask;
>>>>           u32                     start_err;
>>>>           u32                     opendrain;
>>>> +       bool                    dma_lli;
>>>> +       u32                     stm32_idmabsize_mask;
>>>
>>>
>>> What are these?
>>
>>
>> This property is specific for sdmmc variants:
>> sdmmc has a Internal DMA and the number bytes per buffer
>> could be different between sdmmc variants
>> (depend of SDMMC_IDMABSIZER register).
> 
> Okay. Thanks for clarifying.
> 
> Could you please add some information about this in the changelog as well?

OK

> 
> [...]
> 
>>>> +
>>>> +static int _sdmmc_idma_prep_data(struct mmci_host *host,
>>>> +                                struct mmc_data *data)
>>>> +{
>>>> +       int n_elem;
>>>> +
>>>> +       n_elem = dma_map_sg(mmc_dev(host->mmc),
>>>> +                           data->sg,
>>>> +                           data->sg_len,
>>>> +                           mmc_get_dma_dir(data));
>>>> +
>>>> +       if (!n_elem) {
>>>> +               dev_err(mmc_dev(host->mmc), "dma_map_sg failed\n");
>>>> +               return -EINVAL;
>>>> +       }
>>>> +
>>>> +       return 0;
>>>> +}
>>>> +
>>>> +static int sdmmc_idma_prep_data(struct mmci_host *host,
>>>> +                               struct mmc_data *data, bool next)
>>>> +{
>>>> +       /* Check if job is already prepared. */
>>>> +       if (!next && data->host_cookie == host->next_cookie)
>>>> +               return 0;
>>>> +
>>>> +       return _sdmmc_idma_prep_data(host, data);
>>>> +}
>>>> +
>>>> +static void sdmmc_idma_unprep_data(struct mmci_host *host,
>>>> +                                  struct mmc_data *data, int err)
>>>> +{
>>>> +       dma_unmap_sg(mmc_dev(host->mmc), data->sg, data->sg_len,
>>>> +                    mmc_get_dma_dir(data));
>>>> +}
>>>
>>>
>>> The sdmmc_idma_prep_data() and sdmmc_idma_unprep_data(), seems very
>>> similar to what the mmci core driver needs to do in this regards.
>>>
>>> Can we perhaps avoid adding these callbacks altogether, but rather
>>> rely on common code in the mmci core driver?
>>
>>
>> Actually, these callbacks allow to manage prepare/unprepare of
>> dmaengine interface for mmci variant, (not needed for sdmmc which uses an
>> internal dma).
>>
>> For Sdmmc, today there are no special case, just dma_map/unmap.
>> But in the future, I hope manage the lli list in these callback.
>>
>> Only dma_map/unmap could be common, but the error management may
>> be complicated (in mmci variant).
>>
>> Personally, I prefer keep prep_data/unprep_data mmci_host_ops
>> interfaces.
>> What do you suggest ?
> 
> Okay, let's keep them for now. We can always change things on top, in
> case we see later that those callbacks can be removed.

Okay, that make sense.

> 
> [...]
> 
> Kind regards
> Uffe
>