linux-kernel - Re: [PATCH 09/11] mmc: sdhci-cadence: Add Pensando Elba SoC support

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Date:   Thu, 7 Apr 2022 08:45:08 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Brad Larson <brad@...sando.io>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Olof Johansson <olof@...om.net>, dac2@...sando.io,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/11] mmc: sdhci-cadence: Add Pensando Elba SoC support

On Thu, Apr 7, 2022 at 1:36 AM Brad Larson <brad@...sando.io> wrote:
> @@ -350,7 +461,7 @@ static void sdhci_cdns_hs400_enhanced_strobe(struct mmc_host *mmc,
>  static int sdhci_cdns_probe(struct platform_device *pdev)
>  {
>         struct sdhci_host *host;
> -       const struct sdhci_pltfm_data *data;
> +       const struct sdhci_cdns_drv_data *data;
>         struct sdhci_pltfm_host *pltfm_host;
>         struct sdhci_cdns_priv *priv;
>         struct clk *clk;
> @@ -369,10 +480,10 @@ static int sdhci_cdns_probe(struct platform_device *pdev)
>
>         data = of_device_get_match_data(dev);
>         if (!data)
> -               data = &sdhci_cdns_pltfm_data;
> +               data = &sdhci_cdns_drv_data;
>
>         nr_phy_params = sdhci_cdns_phy_param_count(dev->of_node);
> -       host = sdhci_pltfm_init(pdev, data,
> +       host = sdhci_pltfm_init(pdev, &data->pltfm_data,
>                                 struct_size(priv, phy_params, nr_phy_params));
>         if (IS_ERR(host)) {
>                 ret = PTR_ERR(host);
> @@ -389,6 +500,11 @@ static int sdhci_cdns_probe(struct platform_device *pdev)
>         host->ioaddr += SDHCI_CDNS_SRS_BASE;
>         host->mmc_host_ops.hs400_enhanced_strobe =
>                                 sdhci_cdns_hs400_enhanced_strobe;
> +       if (data->init) {
> +               ret = data->init(pdev);
> +               if (ret)
> +                       goto free;
> +       }
>         sdhci_enable_v4_mode(host);
>         __sdhci_read_caps(host, &version, NULL, NULL);

I'm not sure about the abstraction here. The approach of having a single
driver with some platform specific quirks like you do here works fine if the
differences between hardware implementations are fairly minor, but if there
are a larger number of variants, or the differences become too big, the
better approach is to have separate top-level driver instances that call
into a more generic driver, continuing the call chain

elba_drv_init()
 -> sdhci_cdns_probe()
     -> sdhci_pltfm_init()
         -> sdhci_add_host()
             -> mmc_add_host()

with each one being a more specific version of the one below it.
At the moment, it doesn't quite require having a custom driver,
but I fear that it it would get hard to rework if it continues to grow
other front-ends. It may be better to do the abstraction right away,
even if the elba driver becomes rather trivial.

Ulf, any preferences?

         Arnd